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In vitro Regeneration by Indirect Organogenesis of Selected Kenyan Maize Genotypes using Shoot Apices
Abstract
The study reports a reliable and reproducible regeneration system of two open pollinated varieties-OPV`s (Katumani KAT and dry land cultivar DLC1), a hybrid (DH01) and an inbred line (TL08) using shoot apices as explants via organogenesis. The shoot apices were cultured on Murashige and Skoog (MS) basal media supplemented with 9 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 8.88, 17.75, 26.64, 35.52 or 44.40 μM N<sup>6</sup>-benzylaminopurine (BAP) with (+) or without (-) 296 μM adenine for calli induction. The most effective combination for calli induction was modified MS media containing 26.64 μM BAP and 296 μM adenine. Calli was maintained on MS media with 9 μM 2, 4-D and 4.44 μM BAP for calli proliferation. Calli of TL08 genotype directly formed shoots on the media containing 9 μM 2, 4-D and 26.64 μM BAP, while the KAT, DLC1 and DHO1 formed a mixture of embryogenic and organogenic calli on the media supplemented with 9 μM 2, 4-D and 4.44 μM BAP. The frequency of callus formation was genotype dependant with KAT 55%, DLC1 35%, DH01 47% and TL08 44%. The number of shoot formed by the selected varieties ranged from 4.9 to 5.7 shoots depending on the genotypes. The number of shoots formed on the media supplemented with 296 μM adenine was higher than that on media without adenine. Shoots were regenerated from organogenic calli after 4-6 weeks depending on the genotype and the presence or absence of adenine, with plant regeneration varying from between 29-55%. Root induction was promoted using MS media supplemented with 1.97 and 2.95 μM Indole-3-butyric acid (IBA). Seeds from in vitro regenerated plants (R<sub>0</sub>) produced normal plant (R<sub>1</sub>) in the field trial and were comparable to the plants grown with the mother seeds.
... The regeneration of maize plants from immature embryos was first reported in1975 [4]. Consequently, plant regeneration from calli induced from split node explants [12], anthers [23], glume calli [21], immature inflorescences [11], immature tassels [16,19], leaf segments [2,15], seedling segments [17], shoot tips [8,10,26], shoot apical meristems [25] and protoplasts [7] has also been reported successfully. Maintenance and production of immature embryos of maize are challenging and time consuming and they require a well-equipped greenhouse and laborious artificial pollination system. ...
... Among the tested concentrations MS medium supplemented with 1.97 lM IBA induced more number of roots (15.6 ± 0.20) with highest root length (6.5 ± 0.40) (Table 3 ). These results are in accordance with in vitro rhizogenesis studies in maize [8]. All regenerated shoots showed 80% rooting efficiency on IBA medium (Fig. 1gand h) (Table 3). ...
Maize is one of the important cereal crops around the world. An efficient and reproducible regeneration protocol via direct organogenesis has been established using split nodes as ex-plants derived from 7 to 10day old in vitro grown seedlings. Surface sterilized maize seeds were germinated on MS medium lacking plant growth regulators. Nodal sections of 7–10day old seedlings were isolated, split longitudinally into two halves and cultured on regeneration medium containing different concentrations of 6-benzyladenine (2.20, 4.40, 6.60, 8.80, 11.0 and 13.2μM) or kinetin (2.32, 4.65, 6.97, 9.29, 11.6 and 13.9μM). Inclusion of 8.80μM BA into MS supplemented medium triggered a high frequency of regeneration response from split node explants with a maximum number of shoots (12.0±1.15) and the highest shoot length (3.0±0.73) was obtained directly (without an intervening callus phase) within 4weeks of culture. Further shoot elongation was achieved on medium containing 4.40μM BA. The elongated micro shoots were rooted on MS medium fortified with 1.97μM indole-3-butyric acid. The regenerated plantlets with roots were successfully hardened on earthen pots after proper acclimatization under greenhouse conditions. This new efficient regeneration method provides a solid foundation for genetic manipulation of maize for biotic and abiotic stresses and to enhance the nutritional values.
... anthers (Barloy and Beckert 1993), mature embryos (Huang and Wei 2004;Al-Abed et al. 2006), nodal regions (Vladimir et al. 2006), protoplasts (Morocz et al. 1990), glumes (Suprasanna et al. 1986), tassel and ear meristems (Pareddy and Petolino 1990), immature tassels (Songstad et al. 1992), leaves and tassels (Ahmadabadi et al. 2007), shoot tips (O'Connor-Sanchez et al. 2002), shoot meristems (Sairam et al. 2003), and shoot apical meristems (Zhang et al. 2002). Other reports include indirect organogenesis of Kenyan maize using the shoot apex (Muoma et al. 2008). Two reports are available on Indian maize for embryogenesis and indirect organogenesis using nodal regions (Pathi et al. 2013), and indirect organogenesis using immature embryos (Manivannan et al. 2010;Rakshit et al. 2010). ...
... Pathi et al. (2013) reported 9 shoots from mature embryo in HQPM-1 in MS medium containing 8.8 lM BA, 4.6 lM Kin, and 2.6 lM NAA. In Kenyan maize, Muoma et al. (2008) reported 5.7 shoots in KAT and TLO8 from shoot apices in MS medium containing 296 lM adenine, 9 lM 2, 4-D, and 26.64 BA. In China maize, 1.7 shoots were reported in C8605 and 9046 in N6 basal salts containing 2.2 lM BA and 26.64 lM glycine from mature embryo (Huang and Wei 2004). ...
An efficacious regeneration system was developed from shoot apex explants of Zea mays using a two-step culture procedure. Seventeen Indian genotypes were assessed for their regeneration potential. The maximum response of shoot induction was obtained from explants cultured on Murashige and Skoog medium supplemented with 4.5 µM thidiazuron and 26.7 µM glycine. Maximum mean number of shoots (17.2) was observed in genotype COH (m)-5 while NPK was the least responsive (6.7). Shoot clumps transferred from shoot induction medium to multiplication (second) medium amended with 1.1 µM thidiazuron and 0.88 µM N
6
-benzylaminopurine showed increased number of shoots in COH (m)-5 (36.1 shoots); NPK was the least responsive with an average of 9.5 shoots. The best response in root induction, with a larger number of roots (10.5) and longer roots (6.6 cm), was observed in Murashige and Skoog medium supplemented with 7.3 µM indole-3-butyric acid and 7.9 µM phloroglucinol. Analysis of variance indicated that plant regeneration response varied greatly among the genotypes. In vitro raised plants were successfully transferred to the field after hardening, with a 99 % survival rate. Inter simple sequence repeats analysis revealed that the similarity matrix pair-wise value was 1, the Mantel test value was p 1.0; Analysis of molecular variance genetic variances were 93 % within the population and 7 % between populations; Principal component jolliffe cut off was 0.15, Principal component and Principle coordinate analysis % variance was 13.19. These values were congruent for both the mother and the in vitro-raised plants, confirming genetic integrity.
... Efficient use of genetic engineering techniques in the improvement of maize is hampered by the in vitro recalcitrance frequently seen in most cereals making it difficult to induce embryogenic callus and eventual regeneration of maize especially in elite varieties (Ge et al., 2016). Despite this challenge, transformation and regeneration of tropical maize lines and other genotypes including open pollinated varieties and hybrids (Ombori et al., 2008(Ombori et al., , 2013 has been achieved, albeit with some difficulty (Muoma et al., 2008;Oduor et al., 2006;Ombori et al., 2008;Omer et al., 2008). Successful transformation utilizes immature zygotic embryos as explants for indirect transgene delivery often mediated by Agrobacterium tumefaciens (Akoyi et al., 2013;Anami et al., 2010;Mgutu et al., 2011;Ombori et al., 2008). ...
... Report by Pande et al. (2015) stated that optimal multiple shoot induction response was recorded on MS basal media supplemented with 3.0 mg/l of BAP, while Satish et al. (2015) reported 8.3 shoots per explants of finger millet variety 'CO(Ra)-14' in MS basal medium containing 17.6 µM 6 BAP, 0.9 µM2,4-dichlorophenoxyacetic acid (2,4-D) in combination with 750 mg/l proline, 500 mg/l casein enzymatic hydrolysate and 2 mg/l glycine. When compared to other monocots, Pilahome et al. (2014) reported 30.33 shoots per explant of Sakon Nakhon in MS medium containing 50 μM 6-BAP in rice while Muoma et al. (2008) reported 5.7 shoots from inbred lines of Kenyan maize KAT and TLO8 from shoot apices on MS basal medium containing 26.64 µM BAP, 296 µM adenine and 9 µM 2,4-D. Earlier research work on maize genotypes from stated 4.3 shoots (CM300) and 1 to 3 shoots (LM5) in MS medium supplemented with 4.4 µM BA and 2.8 µM IAA from 14-day-old immature embryos (Rakshit et al., 2010;Manivannan et al., 2010). ...
A simple and efficient plant regeneration system via direct organogenesis was established in finger
millet using in vitro derived shoot apical meristems. Six varieties; GBK-043128, GBK-043094, GBK-
043050, GBK-043137, GBK-043122 and GBK-043124 were evaluated. MS medium was used for
cotyledonary germination. Maximum number of shoots (84.33%) was observed in variety GBK-043128
while GBK-043094 had the least germination efficiency (62. 67%). Shoot apical meristems from threeday
old seedlings were evaluated for their potency of shoot induction on varied 6-benzylaminopurine
(BAP) concentrations. Highest shoot induction was observed in medium supplemented with 1.75 mg/l
BAP in GBK-043050 (3.00) whereas GBK-043094 (1.28) had the least response in medium supplemented
with 1.0 mg/l BAP. To induce rooting, in vitro regenerated plants cultured on MS medium was
supplemented with different concentrations of indole-3- acetic acid. The highest response in root
induction, with a larger number of roots (10.28), was observed in MS medium supplemented with 4.0 μM
IAA. Statistical analysis indicated that plant regeneration response varied greatly among the varieties.
In vitro germinated plants were successfully transferred to the greenhouse after hardening, with 300
shoots developing into fertile plants, which were indistinguishable with wild type plants. This plant
regeneration system has potential for production of transgenic finger millet crops.
Key words: Direct organogenesis, finger millet, root induction, shoot apical meristems.
... Report by Pande et al. (2015) stated that optimal multiple shoot induction response was recorded on MS basal media supplemented with 3.0 mg/l of BAP, while Satish et al. (2015) reported 8.3 shoots per explants of finger millet variety 'CO(Ra)-14' in MS basal medium containing 17.6 µM 6 BAP, 0.9 µM2,4-dichlorophenoxyacetic acid (2,4-D) in combination with 750 mg/l proline, 500 mg/l casein enzymatic hydrolysate and 2 mg/l glycine. When compared to other monocots, Pilahome et al. (2014) reported 30.33 shoots per explant of Sakon Nakhon in MS medium containing 50 μM 6-BAP in rice while Muoma et al. (2008) reported 5.7 shoots from inbred lines of Kenyan maize KAT and TLO8 from shoot apices on MS basal medium containing 26.64 µM BAP, 296 µM adenine and 9 µM 2,4-D. Earlier research work on maize genotypes from stated 4.3 shoots (CM300) and 1 to 3 shoots (LM5) in MS medium supplemented with 4.4 µM BA and 2.8 µM IAA from 14-day-old immature embryos (Rakshit et al., 2010;Manivannan et al., 2010). ...
A simple and efficient plant regeneration system via direct organogenesis was established in finger millet using in vitro derived shoot apical meristems. Six varieties; GBK-043128, GBK-043094, GBK-043050, GBK-043137, GBK-043122 and GBK-043124 were evaluated. MS medium was used for cotyledonary germination. Maximum number of shoots (84.33%) was observed in variety GBK-043128 while GBK-043094 had the least germination efficiency (62. 67%). Shoot apical meristems from three-day old seedlings were evaluated for their potency of shoot induction on varied 6-benzylaminopurine (BAP) concentrations. Highest shoot induction was observed in medium supplemented with 1.75 mg/l BAP in GBK-043050 (3.00) whereas GBK-043094 (1.28) had the least response in medium supplemented with 1.0 mg/l BAP. To induce rooting, in vitro regenerated plants cultured on MS medium was supplemented with different concentrations of indole-3-acetic acid. The highest response in root induction, with a larger number of roots (10.28), was observed in MS medium supplemented with 4.0 µM IAA. Statistical analysis indicated that plant regeneration response varied greatly among the varieties. In vitro germinated plants were successfully transferred to the greenhouse after hardening, with 300 shoots developing into fertile plants, which were indistinguishable with wild type plants. This plant regeneration system has potential for production of transgenic finger millet crops.
... Отримана таким способом калусна тканина не має перспектив до подальшого використання, оскільки є нерегенерувальною. Разом із тим, відомі праці, де з успіхом використані сегменти проростків та листків для отримання калусної тканини з наступною регенерацією рослин із неї (Ahmadabadi et al., 2007;Muoma et al., 2008). Після пересаджування на 14-ту добу культивування всіх експлантатів на свіже живильне середовище з одночасним видаленням пророслих пагонів, на 45-ту добу культивування знову фіксували пряму регенерацію (табл. ...
Оцінено здатність до прямого органогенезу сегментів вузлової області пагонів 4-добових проростків ліній кукурудзи селекційної групи Ланкастер. Відзначено особливості прямої регенерації даних експлантатів. Регенерація на 14-у добу культивування сегментів вузлової області пагонів 4-добових проростків відбувається лише шляхом прямого гемогенезу, а на 45-у добу – шляхом прямого гемогенезу та прямого геморизогенезу. Відзначено вплив мінеральної основи живильного середовища на регенераційну здатність у культурі in vitro на 45-у добу культивування. Охарактеризовано сегменти вузлової області пагонів 5-добових проростків як експлантати для отримання ембріогенної калусної тканини та рослин-регенерантів. Відзначено зростання частоти утворення калусної тканини на поверхні вузлової області пагонів проростків при збільшенні тривалості культивування in vitro. Надано рекомендації щодо використання прямого гемогенезу та прямого геморизогенезу у біологічних системах агробактеріальної трансформації.
The genotypic specificities of morphogenesis and regeneration have been studied in vitro in five maize inbred lines from the breeding-promising Lancaster heterotic group, compared with the representatives of other heterotic groups, that is, PLS61, A188, and Chi31. It has been shown that the ratio between the types of morphogenesis, such as organogenesis and embryoidogenesis, in a callus culture is predetermined by the explant genotype and sucrose concentrations in the medium for callusogenesis. The frequency of embryoidogenesis as the most efficient type of morphogenesis, considering further regeneration, was, on average, 40.0 ± 12.8% for maize inbreds from the Lancaster heterotic group and only 14.0 ± 4.0% from other heterotic groups. A sucrose concentration at a level of 30 g/L in the medium for callusogenesis further supported the process of regeneration through embryoidogenesis in inbreds of the Lancaster heterotic group at a level of 26.5 ± 15.4%, while the sucrose concentration of 60 g/L promoted regeneration up to a level of 57.7 ± 19.8%. Contents of sucrose in the medium for callusogenesis in the inbreds representing other heterotic groups did not affect the process of regeneration, and the level of embryoidogenesis with sucrose at the concentrations of 30 and 60 g/L was, respectively, 11.0 ± 7.0 and 15.0 ± 4.8%.
Induction of callus from explants is a critical process in regeneration, micropropagation and transformation of plants. Formation of callus from plant tissues on culture is affected by different factors. This study sought to establish the effect of genotype, source of explants and auxin concentration on callus induction from different Sudanese maize genotypes (222F, Hudiba-1, 441, Giza-2, PR5655 and Mojtamma-45). Callus induction of the six maize varieties was investigated using mature embryos, leaf disks and shoot tips as explants and different concentrations of the auxin; 2,4-dichlorophenoxyacetic acid (2,4-D), ranging from 0 to 10 mg L-1. The highest callus, induction frequency was observed in shoot tips while the lowest was observed in mature embryos. Leaf disks gave a higher callus induction frequency than mature embryos and lower than shoot tips. Concentrations of 2,4-D of 2 mg L-1 gave the highest callus induction for most genotypes while 0 and 10 mg L-1 gave the lowest callus induction for all the genotypes.
Drought affects maize production in Africa leading to up to 70% crop loss and in certain cases total crop loss. Several breeding interventions have been attempted with little success. Thus alternative complementation approaches have been necessitated. The current review looks at genetic engineering as a suitable complement to molecular breeding with emphasis on signal transduction. Complex signaling processes have been exploited and several genes encoding signaling factors that function in the drought response have been identified. The successfully understanding and utility of these upstream transcription factors which demonstrate various signal in adverse condition will greatly enable us effectively exploit these genes. The aim of this review is to understand the molecular mechanism and the function of these genes and to see on how best we can exploit them in current and future studies on development of drought tolerant maize crop.
This is a short review of the classical and new, natural and synthetic plant hormones and growth regulators (phytohormones)
and highlights some of their uses in plant tissue culture. Plant hormones rarely act alone, and for most processes— at least
those that are observed at the organ level—many of these regulators have interacted in order to produce the final effect.
The following substances are discussed: (a) Classical plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene
and growth regulatory substances with similar biological effects. New, naturally occurring substances in these categories
are still being discovered. At the same time, novel structurally related compounds are constantly being synthesized. There
are also many new but chemically unrelated compounds with similar hormone-like activity being produced. A better knowledge
of the uptake, transport, metabolism, and mode of action of phytohormones and the appearance of chemicals that inhibit synthesis,
transport, and action of the native plant hormones has increased our knowledge of the role of these hormones in growth and
development. (b) More recently discovered natural growth substances that have phytohormonal-like regulatory roles (polyamines,
oligosaccharins, salicylates, jasmonates, sterols, brassinosteroids, dehydrodiconiferyl alcohol glucosides, turgorins, systemin,
unrelated natural stimulators and inhibitors), as well as myoinositol. Many of these growth active substances have not yet
been examined in relation to growth and organized developmentin vitro.
Immature embryos of eleven cultivars of hybrid maize (Zea mays L.), cultured on 2,4-D-containing nutrient media, showed rapid proliferation of the scutellum and improved efficiency in the formation of embryogenic callus and somatic embryos. High concentrations of sucrose were found to be most favorable for the formation of the embryogenic callus. Embryoids obtained in cultures of all eleven cultivars germinated in vitro and produced normal green plants which were grown to maturity in soil. The effect of genotype and other factors on somatic embryogenesis in maize are discussed.
Embryogenic callus consisting of both Type 1, firm, compact, translucent, relatively slow growing callus and Type 2, highly friable, rapidly growing callus with well-formed somatic embryos, were observed in elite maize germplasm, notably B73 and hybrids with B73. Parental genotype is very important in the ability to identify and isolate embryogenic callus after 14 and 28 days in culture. A partial diallel analysis revealed that a large proportion of the genotypic variation was of the additive type although heterosis did positively increase culture response in most cases. A significant negative maternal effect for culture response was noted for inbred B73 from Reid-type germplasm while four lines sampled from Lancaster germplasm showed similar response whether used as male or female. Although significant media differences were observed in some genotypes, culture media did not preclude observation of Type 1 or Type 2 embryogenic cultures in this study after 14 and 28 days. Plants could be regenerated from all genotypes in this study after 14-days of culture, but not all genotypes were capable of sustained subculture and plant regeneration. Plant regeneration from Type 2 cultures of B73 and B73 hybrids has been obtained up to a year after initiation.
Protoplasts isolated from a totipotent embryogenic cell suspension culture of Zea mays L. (cultivar 'Dekalb XL82') underwent sustained cell divisions when cultured in liquid as well as agarose media. Optimal colony formation (5%) occurred in a liquid medium containing 0.5 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). A soft and unorganized callus was formed when the protocolonies were transferred to agar solidified suspension maintenance medium. Compact, organized and yellow to pale green folded structures and somatic embryos were formed upon subsequent transfer of this callus to a low 2,4-D medium. Clusters of somatic embryos germinated precociously but no plants were recovered.
The frequency of initiation of friable, embryogenic callus from immature embryos of the elite maize inbred line B73 was increased dramatically by introgression of chromosomal segments from the inbred line A188 through classical backcross breeding. Less than 0.2% of the immature B73 embryos tested (5 of 3,710) formed embryogenic callus. The breeding scheme consisted of six generations of backcrossing to B73 with selection at each generation for high frequency initiation of embryogenic cultures. BC6 individuals were selfed for four generations to select homozygous lines. The average embryogenic culture initiation frequency increased to 46% (256/561). Nearly all (91%) of the embryos from one BC6 S4 plant formed embryogenic cultures. RFLP analysis was used to determine the locations and effects of the introgressed A188 chromosomal segments. Five segments were retained through at least the fifth backcross generation. The hypothesis that one or more of these five regions contains genes controlling somatic embryogenesis in maize was tested using an F2 population of the cross A188 X Mo17. A set of five DNA markers (three of them linked) explained 82% of the observed phenotypic variance for percentage of immature embryos forming embryognic callus. Four of the five markers were located in or near introgressed A188 chromosome segments.
The region marked by probe c595 on the long arm of chromosome 9 was highly associated with several measures of in vitro culture response (percent embryogenic embryos, plants per embryo, and plants per embryogenic embryo). We propose that there is a major gene (or genes) in this region in A188 that promotes embryogenic callus initiation and plant regeneration in B73, Mo17, and probably many other recalcitrant inbred lines of maize.
Maize Type II callus tissue was used as the plant material for genetic transformation via electroporation. Plasmid DNA containing a selectable marker gene (either neomycin phosphotransferase (npt-II) or phosphinothricin acetyl transferase (bar)), and a screenable marker gene (gus A) was incubated with the tissue prior to electroporation. Electroporated callus tissue was placed on selection medium containing kanamycin sulfate or Bast(™). No kanamycin resistant colonies were recovered whereas four independent Basta(™) resistant callus isolates were recovered from a total of 544 cuvettes electroporated. After 8 to 16 weeks on the Basta(™) containing medium, selected calli were isolated and maintained in individual selection plates for 4 to 6 weeks until sufficient tissue accumulated. Enzyme assays and DNA analyses were performed to verify the transformation events. Several plants were regenerated from individual callus isolates. The plants derived from one callus isolate were male sterile while those derived from the other isolates were both male and female fertile. Most plants showed Basta(™) resistance. DNA analyses confirmed the presence of the introduced bar gene(s) in the primary regenerants and their progeny. The integration patterns of the inserted DNA appeared to be complex.
In-vitro methods have been developed to regenerate clumps of multiple shoots and somatic embryos at high frequency from shoot tips of aseptically-grown seedlings as well as from shoot apices of precociously-germinated immature zygotic embryos of corn (Zea mays L.). About 500 shoots were produced from a shoot tip after eight weeks of culture (primary culture and one subculture of four weeks) in darkness on Murashige and Skoog basal medium (MS) supplemented with 500 mg/L casein hydrolysate (CH) and 9 μM N(6)-benzyladenine (BA). In this medium, shoots formed in shoot tips as tightly packed "multiple shoot clumps" (MSC), which were composed of some axillary shoots and many adventitious shoots. When the shoot tips were cultured on MS medium containing 500 mg/L CH, 9 μM BA and 2.25 μM 2,4-dichlorophenoxyacetic acid (2,4-D), most of the shoots in the clumps were adventitious in origin. Similar shoot tips cultured on MS medium containing 500 mg/L CH, 4.5 μM BA and 2.25 μM 2,4-D regenerated many somatic embryos within eight weeks of culture. Somatic embryos were produced either directly from the shoot apical meristems or from calli derived from the shoots apices. Both the MSC and the embryos produced normal shoots on MS medium containing 2.25 μM BA and 1.8 μM indole-3-butyric acid (IBA). These shoots were rooted on MS medium containing 3.6 μM IBA, and fertile corn plants were grown in the greenhouse. The sweet-corn genotype, Honey N Pearl, was used for the experiments described above, but shoot-tip cultures from all of 19 other corn genotypes tested also formed MSC on MS medium containing 500 mg/L CH and 9 μM BA.
Setosphaeria turcica (Luttrell) Leonard and Suggs causes northern corn leaf blight (NCLB), an important disease of maize (Zea mays L.) in sub-Saharan Africa and other tropical and temperate regions. Quantitative trait loci (QTL) for resistance were mapped and characterized in a population of F(2:3) lines derived from a cross between the susceptible line Lo951 and the highly resistant CIMMYT line CML202, and tested in three inoculated trials in Kenya (n = 194-256 lines). Incubation period (IP) and area under the disease progress curve (AUDPC, based on three readings) were assessed. Both traits showed a continuous distribution in the population with no transgressive segregation. Variance components for genotypes (G) and environments (E) were highly significant for both traits. G x E interaction was also significant but less important. Heritability was 0.86 for IP and 0.81 for AUDPC. Genotypic and phenotypic correlations between IP and AUDPC were tight (r(g) = -0.84, r(p) = -0.71). The genetic map encompassed 110 RFLP marker loci with an average interval length of 17 centimorgans (cM). Composite interval mapping revealed different but overlapping sets of QTL in the individual environments. In the combined analysis, 10 QTL were detected for IP and AUDPC. These included two QTL with resistance alleles coming from the susceptible parent, Lo951. Six QTL (on Chromosomes 2, 3, 5, 8, 9) were associated with both traits, two affected only IP, another two only AUDPC. The QTL explained 61% of the genotypic and 52% of the phenotypic variance of IP (AUDPC: 69 and 56%). The magnitude of the individual QTL effects was homogeneous and their gene action additive. Marker-assisted improvement of NCLB resistance is considered feasible, though not necessarily economically viable.
This paper focuses on the impact of Striga spp. on maize production and the use of biotechnology (e.g. transgenics, tissue culture, Bt genes, and transposon-transmitted suicide (inducible) genes) to control the damage caused by Striga spp. The use of biocontrol measures to Striga control is briefly discussed.
The developmental histology of somatic embryo (=embryoid) formation in cultured immature embryos of hybrid maize cultivars (Zea mays L.) is described. Embryos cultured on media containing 2% sucrose formed distinct globular embryoids. These embryoids arose either directly by divisions confined to the epidermal and the subepidermal cells at the coleorhizal end of the scutellum or from a soft and friable embryogenic callus produced by them. On media containing 6% sucrose divisions were initiated in the cells adjacent to the procambium of the cultured embryos. Subsequently, zones of meristematic cells also were observed in the region of the node and in the basal portion of the scutellum. Mature, well organized somatic embryos as well as a compact nodular type of embryogenic callus were produced as a result of localized meristematic activity along the tip of the scutellum toward the coleorhiza. Some embryos formed only the compact type of callus, and shoot primordia were organized later in the surface layers of this callus.