Arachis inflata: A New B Genome species of Arachis (Fabaceae)

Abstract

Great efforts have been done to collect germplasm of the Arachis genus in South America, however, many regions still remain underexplored. Under the hypothesis that these regions have new and diverse populations/species of Arachis, several expeditions were carried out since 2000 in Bolivia, to increase the documentation of the genus diversity. As a first result of these explorations, a new species of section Arachis with B genome is formally described. Arachis inflata is closely related to A. magna and A. ipaënsis, but it can be clearly distinguished from them, and from any other species of the genus, for having a type of fruit with a completely distinct morphology. The fruit has a smooth epicarp, but shows a bullated aspect, due to the presence of air chambers in the mesocarp.

Full text

1
G. J. Seijo et al., A new B genome species of Arachis
1 Instituto de Botánica del Nordeste (IBONE, UNNE-CONICET), Facultad de Ciencias Agrarias, Campus Cabral,
Corrientes, Argentina. E-mail: J. G. Seijo: jgseijo@yahoo.com
2 Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste, Campus Deodoro Roca,
Corrientes, Argentina.
3 Herbario Forestal Nacional Martín Cárdenas (BOLV), Centro de Biodiversidad y Genética, Universidad Mayor de
San Simón, Cochabamba, Bolivia.
4 Professor Emeritus, Texas A&M AgriLife Research, Texas A&M University, Stephenville, TX 76401, USA.
 
Arachis inata: una nueva especie de Arachis (Fabaceae) del Genoma B
Guillermo J. Seijo1,2 , Margoth Atahuachi3, Charles E. Simpson4 & Antonio Krapovickas1
Summary: Great eorts have been done to collect germplasm of the Arachis genus in South
America, however, many regions still remain underexplored. Under the hypothesis that these
regions have new and diverse populations/species of Arachis, several expeditions were carried
out since 2000 in Bolivia, to increase the documentation of the genus diversity. As a rst result
of these explorations, a new species of section Arachis with B genome is formally described.
Arachis inata is closely related to A. magna and A. ipaënsis, but it can be clearly distinguished
from them, and from any other species of the genus, for having a type of fruit with a completely
distinct morphology. The fruit has a smooth epicarp, but shows a bullated aspect, due to the
presence of air chambers in the mesocarp.
Key words: Germplasm, peanut, Planalto Chiquitano.
Resumen: Se han realizado grandes esfuerzos para coleccionar germoplasma del género
Arachis en Sudamérica, sin embargo, aún quedan muchas regiones subexploradas. Bajo
la hipótesis de que estas tienen poblaciones/especies nuevas y diversas de Arachis, se
realizaron nuevas expediciones en Bolivia a partir del año 2000 con el objetivo de incrementar la
documentación de la diversidad de este género. Como primer resultado de estas exploraciones,
en este trabajo se describe formalmente una nueva especie de la sección Arachis perteneciente
al genoma B. Arachis inata es una especie afín a A. magna y A. ipaënsis, aunque se distingue
claramente de ellas, y de todas las demás especies del género, por presentar un tipo de fruto
distinto. El mismo presenta epicarpo liso, con aspecto ampollado, debido a la presencia de
cámaras de aire en el mesocarpo.
Palabras clave: Germoplasma, maní, Planalto Chiquitano.
Introduction
Section Arachis is the largest and more
diverse taxonomic section of the homonymous
genus (Krapovickas et Gregory 1994; Valls
et Simpson 2005). It is composed of 31
     
 
chromosome numbers (x= 9, 10) and ploidy
(2x and 4x) levels (Smartt et al., 1978; Gregory
et Gregory, 1979; Fernández et Krapovickas
1994; Stalker, 1991; Seijo et al., 2004, 2007;
Robledo et Seijo, 2008, 2010; Robledo et al.,
2009; Silvestri et al. 2015). Germplasm of
these wild species (mainly with 2n= 2x= 20) is
economically important, because they are the
Seijo, G. J., M. Atahuachi, C. E. Simpson & A. Krapovickas. 2021. Arachis inata: A New B Genome species of Arachis
(Fabaceae). Bonplandia 30(2): 1-6.
Doi: http://dx.doi.org/10.30972/bon.3024942 Recibido 23 Febrero 2021. Aceptado 7 Abril 2021.
Publicado en línea: 10 Junio 2021. Publicado impreso: 15 Agosto 2021.
ISSN 0524-0476 impreso. ISSN 1853-8460 en línea.

2
BONPLANDIA 30(2). 2021
most related to the cultivated peanut (2n= 4x=
40, AABB) and have several potentially useful
agronomic traits for genetic improvement of
the crop (Simpson, 2001; Stalker et al., 2016).
Intense germplasm collections were carried
out in Argentina, Brazil and Uruguay enlarging
the number of accessions maintained in the

Institutions to the present day. Even though
several exploration missions for wild Arachis
species were done in Bolivia, most of them
concentrated in the 70´s - 80´s and early 90’s
      
      
that required the expeditions at that time
resulted in a sparse picture of many of the
collection points. Despite the comparatively
few expeditions, most of the species of section
Arachis were found in Bolivia, and most of
them are endemic, indicating that this country
is a large center of diversity for this group of
plants and deserves more attention.
Under the hypothesis that underexplored
areas have new and diverse populations/
species of Arachis, we conducted a series
of explorations since 2000, mainly in the
Santa Cruz department of Bolivia, with the
objective of increasing the documentation of
the genus diversity. Those explorations were
only possible thanks to the collaboration of
researchers from the Instituto de Botánica
del Nordeste in Corrientes (Argentina) with
those from the Herbario Nacional de Bolivia
in La Paz (LPB), Herbario Nacional Forestal
Martín Cardenas (BOLV) in Cochabamba, and
Herbarium of the Museo de Historia Natural
      
Sierra (USZ), all from Bolivia; also, with the
collaboration of researchers from Texas A&M
AgriLife Research, USA and Embrapa Genetic
Resources and Biotechnology (CEN, Brazil).
Herbarium acronyms follow Thiers (2021).
A first result of these explorations
is the finding of Arachis populations that
undoubtedly belong to a new B genome
species of section Arachis. While searching
for Arachis species in the Planalto Chiquitano,
Velazco Province, Santa Cruz Department,
several new populations of A. magna (e.g. J.
G. Seijo, V. G. Solís Nea, A. Schinini & R.
Almada 2996, 3022 and J. G. Seijo & V. G.
Solís Nea 3257, 3289; all at LPB and CTES)
were found. Also, some other populations
were found (like J. G. Seijo, V. G. Solís Nea,
M. Grabiele & W. Reynoso 3637, 3640, 3649,
3653, 3664, 3790) that resemble A. magna in
the aerial organs, although they looked larger
       
above-ground vegetative organs revealed that
        
axis of well developed plants was wider and
less acute than in A. magna, and the margin of

presence of a dense layer of long hairs. Also,
in most of the populations the color of the
standard petal was pale orange compared to
the intense orange tone commonly observed in
A. magna and other Arachis species of the B
genome. The great surprise came after sifting
the soil. The fruit articles recovered were
     
A. magna, with reticulated morphology. They
were very large, with a smooth epicarp, and
with air chambers in the mesocarp, that gave
them a bullated external appearance (Fig. 1
G-H).
Further studies of the morphology,
    
cross compatibility of these accessions with
bullated fruits provided evidence that they
belong to a new species of section Arachis.
Here we present its formal description in the
following section.
  Seijo, Atahuachi, C. E.
Simpson & Krapov.  Fig. 1.
Morphologically similar to Arachis magna
Krapov., W. C. Greg. & C. E. Simpson, but
differing by the generally larger plants,
less acute leaets and with whitish margin,
and bullated, not reticulated, fruits, with
conspicuous air chambers in the mesocarp.
Typus. Bolivia. Santa Cruz:  
de Chávez, 4,2 km S de San Antonio de
Lomerío, camino a San Juan de Lomerío,
16º48’01”S, 61º50’24”W, 343 m, 21-I-2005,
J. G. Seijo, V. G. Solís Nea, M. Grabiele &
W. Reynoso 3637 (holotypus CTES, isotypus
LPB).

3
G. J. Seijo et al., A new B genome species of Arachis
Fig. 1. Arachis inata (Seijo et al. 3637). A: Main axis and a lateral branch of a young plant. Note remains of the fruit (that
harbored the seed that gave rise to the plant) in the roots. B: Stem. C: Lateral branch apex. D: Main stem apex. E: Detail of the apex

with a bullated aspect. H: Inside view of half fruit article with the seed removed. Note the bullated aspect in the inner surface of the
fruit article and the air chambers in the mesocarp (some of them were manually opened). Drawings by Liliana Gómez.
Fig. 1. Arachis inata (Seijo et al. 3637). A: Eje principal y rama lateral de una planta joven. Se observan restos del fruto (que
contenía la semilla que dio origen a la panta) en las raíces. B: Tallo. C: Ápice de la rama lateral. D: Ápice del eje principal. E:
      
externa de un artejo del fruto, el exocarpo con aspecto ampollado. H: Vista interna de una mitad de artejo con la semilla removida.
Se observa el aspecto ampollado en la cara interna de artejo y las cámaras de aire en el mesocarpo (algunas de ellas fueron
manualmente abiertas). Ilustración realizada por Liliana Gómez.

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BONPLANDIA 30(2). 2021
Annual herb, weak axonomorphic root.
Mainstem erect, up to 90 cm long, usually
       
branches at the base. Lateral branches
prostrated, up to 1.50 m long, stems green,
rounded, or somewhat angular, quadrangular in
dried specimens, villous, with wavy hairs 1.5-
2 mm long, and few scattered bristles. Leaves
tetrafoliolate. On the main-stem, stipules with
the fused portion 14-20 mm long, the free
part 28-40 mm long, 2.5-3 mm wide at the
base; petiole 35-55 mm long; rachis 10-20
  
basal pair 45-52 mm long, 18-24 mm wide,
and the apical one 52-63 mm long, 22-28 mm
wide. On lateral branches, the fused part of the
stipules 5-13 mm long, and the free part 15-
22 mm long, 2.5-3.5 mm wide; petiole 12-22

to cordate, obtuse to sub-acute, proximal pair
23-30 mm long, 15-20 mm wide, distal one
28-33 mm long, 19-22 wide. The fused part
of the stipules villous, with long wavy hairs
and long bristles, the free portion glabrous
in most of the surface with few long hairs
and bristles toward the base, margins ciliate.
Petiole and rachis canaliculated, villous and
  
glabrous, abaxial face with sparse adpressed
1 mm long hairs, and wavy 1-2 mm long
hairs in the midvein, margin densely ciliate
with antrorse white hairs and few 1 mm long
     
spikes, hypanthium 30-60 mm long, light
pink, covered with 1-2 mm long wavy hairs.
Calyx light pink, villous with some sparse
long bristles; upper lip 4-5 mm long; lower lip
falcate, narrow, 5-6 mm long. Standard petal
9-10 mm long, pale orange, with orange lines
on the front and yellow throat, wings yellow
and keel whitish. Peg violaceous, villous in
the aerial part, with wavy 1-2 mm long and
scattered 1-2 mm long adpressed hairs. Fruit
subterranean, biarticulated, articles ellipsoid,
15-25 mm long, 10-14 mm wide, without beak,
surface smooth, bullated due to air chambers in
the mesocarp. Shell thick, up to 5 mm.
Chromosome number: 2n= 20, without large
heterochromatic bands in the typical accession
Seijo et al. 3637 (Seijo unpublished).
Geographic distribution and habitat: It
grows in Santa Cruz Department (Bolivia),
Ñuflo de Chávez and Velasco provinces,
Lomerío region, in the southern portion of the
Planalto Chiquitano, and the northern part of
the San Julian River Basin, which in turn drains
into the Mamoré River. Most populations were
found in the undergrowth of cerrado vegetation
or in the transition between cerrado vegetation
and open grassy patches, close to lagoons or
water courses, in sandy soils.
Etymology
air chambers present in the mesocarp that gives

Paratypi:    Prov.
  
Lomerío a San Juan de Lomerío, 16º48’02”S,
61º50’26”W, 328 m, 29-XI-2007, Atahuachi
et al. 1390 (BOLV, CTES); 6,9 km S de
San Antonio de Lomerío, 16º48’30”S,
61º51’10”W, 390 m, 31-I-2005, Seijo et al.
3640 (CTES, LPB, UCZ); id., 16º48’36”S,
61º51’12”W, 29-XI-2007, Atahuachi et al.
1391 (BOLV, CTES); 18,1 km S de San
Antonio, 16º52’04”S, 61º50’16”W, 417 m,
21-I-2005, Seijo et al. 3649 (CTES, LPB);
id., Itotoca, 16º52’05”S, 61º50’13”W, 383 m,
29-XI-2007, Atahuachi et al. 1393 (BOLV,
CTES); 23,1 km S de San Antonio, 16º54’S,
61º49’W, 21-I-2005, Seijo et al. 3653 (CTES,
LPB); 39,8 km S de San Antonio, 16º58’31”S,
61º48’28”W, 290 m, 21-I-2005, Seijo et al.
3664 (CTES, LPB). Prov. Velasco, 31,2 km
S de San Rafael, 17º01’S, 60º36’W, 302 m,
8-IV-2004, Seijo & Solís Nea 3292 (CTES);
89,4 km NE de San Ignacio, 16º15’23”S,
60º15’52W, 280 m, 25-I-2005, Seijo et al.
3715 (CTES, LPB); 32 km S de San Rafael,
camino a San José, 17º01’S, 60º36’W, 288
m, 1-II-2005, Seijo et al. 3790 (CTES, LPB);
camino San Rafael-Las Petas, Hacienda San
Jorge, 16º38’18”S, 59º59’31”W, 212 m, 30-
XI-2007, Atahuachi et al. 1405 (BOLV,
CTES).
Obs. 1: The area of A. inata is associated
with the Planalto Chiquitano, overlaps the SW
area of A. magna and extends southward to the
San Julian River. The above-ground vegetative

5
G. J. Seijo et al., A new B genome species of Arachis
appearance is similar in both species, however,
they are easily distinguished by the morphology
of the fruit: while A. magna has the classical
reticulated ones, A. inata has fruits that bear
conspicuous air chambers in the mesocarp,
giving the external appearance of a bullated
surface. The later character of the fruit is unique
in the genus Arachis   
color of the standard petal, while in A. inata it
is pale orange, in A. magna is of a more intense

well, in A. magna is poorly distinguishable while
in A. inata is conspicuously whitish, due to the
presence of abundant long hairs.
Obs. 2: Arachis inata does not have large
heterochromatic bands in its chromosomes and
has a typical karyotype of the B genome species,
resembling that of A. magna and A. ipaënsis
(Seijo et al. unpublished). Crossing data gave the
following pollen stain results with A. inata × A.
ipaënsis (K 30076) 61.3%; A. magna (V 13761)
45.4%; A. glandulifera (K 30091) 11.8%; A.
krapovickasii (Wm 1291) 8.6%; A. batizocoi
(K 9484) 2.93%. These data help to solidify the
separation of A. inata into a new species.
Obs. 3: Moretzhon et al. (2012) studied the
genetic relationships among species of section
Arachis, including the accession Seijo et al.
3292 of A. inata, by using intron sequences
of a few nuclear genes and SSR markers. This
accession of A. inata grouped closely with an
accession of A. williamsii in the cluster made
on intron sequences, but with a set of A. magna
(sister to accession V14750) in the distance tree
  
A. inata belongs to the B genome and that there
is a very low genetic distance among species in
this group.
Acknowledgements
We acknowledge to the Myndel Botanica
Fundation for providing funds to support the
expeditions in Bolivia in 2004, 2005 (to GS) and
in 2012 (to MA) and to Agencia Nacional de

for contributing with funds to these expeditions
and for the characterization of the materials
collected (Projects PICT-2012-1875 and PICT-
2018-03664 to GS). We also acknowledge
to all the collectors that participated in the
expeditions for their help in the fieldwork.
We especially thanks to Stephan Beck of LPB
who made possible the initial collaborations
between Argentinian and Bolivian institutions.

the collection permits to carry out this work is
greatly appreciated. The drawing of A. inata
is greatly acknowledged to Liliana Gómez,

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