Inheritance of albinism in certain interspecific and intersubspecific crosses in groundnut (Arachis hypogaea L.)

Summary A study of the several interspecific and inter-subspecific crosses indicated that albinism in groundnut is recessive and in these crosses is controlled by triplicate recessive loci.ICRISAT Paper No. JA-336     

The role of mutations in intraspecific differentiation of groundnut (Arachis hypogaea L.)

Summary Based on morphological diversity, cultivated groundnut (Arachis hypogaea L.) is classified into two subspecies (fastigiata and hypogaea) and further into four botanical types (Spanish bunch, Valencia, Virginia bunch and Virginia runner). In a cross between two Spanish cultivars belonging to ssp. fastigiata, a true breeding variant (Dharwad early runner) sharing some characters of both the subspecies was isolated. The variant, on mutagenesis with ethyl methane sulphonate (EMS) yielded a very high frequency of mutants resembling all four botanical types. Some of the mutants produced germinal reversions to Dharwad early runner in later generations indicating genetic instability. While most of the revertants bred true, some of the mutants continued to segregate, wherein each botanical group of mutants produced all other botanical types. A detailed analysis of the breeding behaviour of mutants revealed several unusual features (such as homozygous mutations, mutation outbursts, segregation distortions, somatic mutations and multiple character mutations) that could not be explained through conventional mutation theory. In the light of these findings, the role of mutations in evolutionary differentiation of the crop and the probable mode of their origin have been discussed.     

Inheritance of two components of early maturity in groundnut (Arachis hypogaea L.)

Summary Knowledge of inheritance of early maturity or its components is important to groundnut breeders in developing short-duration cultivars. This study was conducted to determine the inheritance of two components of early maturity: days to first flower from sowing, and days to accumulation of 25 flowers from the appearance of first flower, using three groundnut genotypes. Two early-maturing (Chico and Gangapuri) and one late-maturing (M 13) genotypes were crossed in all possible combinations, including reciprocals. The parents, F₁, F₂, F₃, and backcross populations were evaluated for days to first flower from sowing, and for days to accumulation of 25 flowers. The data suggest that days to first flower in the crosses studied is governed by a single gene with additive gene action. Chico and Gangapuri possess the same allele for this component of earliness. Three independent genes with complete dominance at each locus appear to control the days to accumulation of 25 flowers. In crosses between late (M 13) and early (Chico or Gangapuri) parents, a segregation pattern suggesting dominant-recessive epistasis (13 late:3 early) was observed for this component. Segregation in the F₂ generation (1 late:15 early) of both early parents (Chico x Gangapuri) indicated that the genes for early accumulation of flowers in these two parents are at different loci.Submitted as ICRISAT J.A. No. 1557.     

Reciprocal cross differences in a 6×6 diallel set of groundnut (Arachis hypogaea L.) in the F1 generation

Summary Reciprocal cross differences were studied in a 6×6 diallel full set comprising of thirty hybrid combinations of groundnut in the F₁ generation.Reciprocal cross differences were observed for growth habit in four pairs of crosses, for leaf colour, flower colour and stem pigmentation in two pairs of crosses each. It was observed that the inheritance of flower colour, stem pigmentation and testa colour which exhibited different shades of purple colour was likely to be governed by pleiotropic gene(s). Among the quantitative characters significantly positive reciprocal effects were observed in different crosses for number of mature pods per plant, weight of pods per plant and shelling percent. Marked reciprocal cross differences were observed for pod and kernel characters like pod filling, pod beak, pod constriction and testa colour.     

Genetics of nonnodulation in groundnut (Arachis hypogaea L.). Studies with single and mixed Rhizobium strains

Summary Genetic studies of nonnodulation in groundnut were carried out in a cross, NC 17×PI 259747, with a single Rhizobium strain, NC 92, and a native Rhizobium population.The normal nodulation of the parents, F₁ generations and backcross progenies, and the F₂ segregation for nodulation and nonnodulation confirmed that nonnodulation in groundnut is controlled by two duplicate recessive genes.Approved ICRISAT Journal Article No. 211.     

Components of resistance to late leaf spot and rust among interspecific derivatives and their significance in a foliar disease resistance breeding in groundnut (Arachis hypogaea L.)

Late leaf spot (LLS) and rust cause substantial yield losses and reduce the fodder and seed quality in groundnut (Arachis hypogaea L.). Adoption of resistant cultivars by the semi-arid tropic farmers is the best option to overcome yield losses. Knowledge on components of resistance to these diseases should facilitate the development of groundnut cultivars with enhanced resistance to LLS and rust. The objectives of the experiments were to study the genetic variability and relationships among components of resistance to LLS and rust, and assess their significance in disease resistance breeding. Fifteen interspecific derivatives for LLS and 14 for rust and a susceptible control, TMV 2, were evaluated in a randomised complete block design with two or three replications under greenhouse conditions. The experiments were repeated twice. Genotypic differences were highly significant for all the traits studied. Resistance to LLS is due to longer incubation and latent periods, lesser lesions per leaf, smaller lesion diameter, lower sporulation index, and lesser leaf area damage and disease score. Selection based on components of resistance to LLS may not lead to plants with higher retained green leaf area. The remaining green leaf area on the plant should, therefore, be the major selection criteria for resistance to LLS in breeding programs. Resistance to rust is due to longer incubation and latent periods, fewer pustules per leaf, smaller pustule diameter, lower sporulation index, and lesser leaf area damage and disease score. Rust resistant components appear to work additively, therefore, selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs. ICGV 99005, 99003, 99012, and 99015 for rust and ICGV 99006, 99013, 99004, 99003, and 99001 for LLS are the better parents for use in resistance breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytoplasmic-genetic male sterility in radish (Raphanus sativus L.). Identification of maintainers,inheritance of male sterility and effect of environmental factors

Summary Research has been carried out on identification of maintainers for cytoplasmic-genetic male sterile lines in Japanese and European radish, on the mode of inheritance of male sterility and on the effect of environmental factors on the expression of this character.In a Japanese radish population and in most early European radish populations maintainers were found in high frequency. Segregations for male sterility in full-sib families, obtained by crossing male sterile and male fertile plants, and in backcross generations, indicated that male sterility is probably determined by one dominant and two recessive independently acting genes, but also minor genes may be involved.The expression of male sterility was not affected by seasonal influences. In some populations a reversible temperature effect was found, most ms plants occurred at 10, 14 and 26°C and most mf plants at 17 and 20°C.     

Heterosis in relation to genetic divergence and specific combining ability in groundnut (Arachis hypogaea L.)

Summary The frequency and magnitude of heterosis were examined in relation to genetic divergence among parents in two diallel cross experiments in groundnut. The parents were grouped into clusters based on their diver-gence. The range, mean and standard deviation of the intra-and inter-cluster divergence were used to define four divergence classes. The frequency of heterotic crosses and the magnitude of heterosis for yield and its components were found to be higher in crosses between the parents in intermediate divergence classes than extreme ones. The results agreed well with the overall status of the specific combining ability of these crosses.     

Cytology and leafspot resistance in Arachis hypogaea x wild species hybrids

Summary Introgression of germplasm from diploid wild Arachis species to A. hypogaea has great potential for improving pest resistance in cultivated peanuts. This investigation evaluated methods for incorporating exotic germplasm into cultivated peanuts, especially for Cercospora arachidicola Hori resistance. Interspecific hybrids between A. hypogaea (cvs. NC 2 and NC 5) and the wild species A. cardenasii Krap. et Greg. nom. nud. and A. chacoense Krap. et Greg. nom. nud. were analyzed cytologically and for leafspot resistance. All F₁ hybrids were sterile, had irregular meiosis, and very few multivalents. They were highly resistant to C. arachidicola in field tests and had a 10-fold reduction of conidia per lesion in the greenhouse as compared to A. hypogaea cultivars. After colchicine treatments of F₁ hybrids, hexaploids (2n=60) and aneuploids (2n=54, 56, 63) were observed. The hexaploids had up to 18 univalents per pollen mother cell and very few multivalents, indicating a low frequency of intergenomic chromosome pairing. For C. arachidicola resistance, significant differences were not found among wild species parents, F₁ hybrids and two generations of hexaploids. Most hexaploids were stable at 2n=60 and embryos aborted when backcrosses with the respective wild species were attempted. However, when hexaploids were backcrossed to A. hypogaea, several fertile pentaploid (2n=50) offspring were obtained. Use of self-pollinating pentaploids is believed to be the quickest method to recover 40-chromosome hybrid derivatives in these hybrids.     

Frequencies of plasmon types in a germ plasm sample of peanuts,Arachis hypogaea

Summary The plasmon constitution of 68 different accessions of cultivated peanuts (Arachis hypogaea L.) was studied in crosses with one or another of three testers: V4, VSM and HG1, having the [V4], [O] and [G] plasmons, respectively. The plasmons interact differently with three plasmon-sensitive nuclear genes, thereby determining whether the plants will be erect or trailing. From the phenotypes of the reciprocal F₁ hybrids it was concluded that the [G] plasmon of HG1 is rare-it is present in this cultivar and possibly in a few other; the [V4] plasmon is rare, being present in the V4 cultivar and possibly in a few other accessions; the [O] plasmon is widespread, being present in lines from various geographical origins and in at least three of the four botanical types of cultivated peanuts.     

Early generation testing for yield and physiological components in groundnut (Arachis hypogaea L.)

Selection of superior crosses of groundnut (Arachis hypogaea L.) in early generations would increase the probability of identifying superior lines. The objective of this study was to determine the potential of selecting for physiological traits identified in a yield model [crop growth rate (C), reproductive duration (DR) and partitioning (p)] in segregating populations. Forty populations and nine parental lines were evaluated in replicated trials in 1992 (F2, 1993 (F3) and 1994 (F4) at three locations in Niger. Physiological traits were estimated from final yield and biomass as well as data on flowering and maturity. Regressions from two different parent-offspring generations (F2: F3 and F3: F4) were calculated. The results were compared to determine if early generation performance accurately predicts the performance of cross bulks in later generations. Differences were observed among populations and parents for all traits. Effects of locations were significant for C, p and DR in F2 and F3 but nonsignificant for yield and C in F4. Regression coefficients from F3: F2 were 0.10 ± 0.08 for C, 0.45 ± 0.17 for p, 0.10 ± 0.03 for DR and 0.16 ± 0.03 for pod yield. Based on F3: F4 regression, the coefficients were 0.12 ± 0.23 for C, 0.46 ± 0.17 for p and 0.57 ± 0.17 for yield. Parent-offspring correlations were in most cases similar to the regression values. It was concluded that selection for yield and model components in early generation bulks may inneffective. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of diallel cross for some physical-quality traits in peanut (Arachis hypogaea L.)

The combining abilities for physical-quality traits in peanut were examined to understand the type of gene action governing these traits, and to identify peanut genotypes suitable for use as parents in breeding for quality improvement. The F₁ hybrids including reciprocals from a six-parent diallel cross along with the parents were evaluated in a randomised complete block design. Data were recorded on five quality traits in peanut viz., shelling outturn, 100-pod weight, 100-seed weight, Count and proportion of sound mature seeds. Substantial genetic variability was observed among the hybrids for the traits studied. Diallel analysis indicated that expression of majority of the quality traits is regulated predominantly by additive gene action suggesting possibility of early-generation selection, while non-additive gene action also plays an equally important role in the control of seed size. Significant reciprocal effect for all the traits denoted role of maternal parent in the expression of quality traits and importance of parental selection in quality breeding. Genotypes ICGV 86564 and TPG 41 were good combiners for seed size, while J 11 was a good combiner for improvement of shelling outturn and proportion of mature seeds. Association between general combining ability (GCA) effects and mean performance suggested that the performance per se of the genotype should be a good indicator of its ability to transmit the desirable quality attributes to its progenies. Though performance of crosses was found to be independent of parental GCA status, it is evident that at least one of the parents used in hybridisation should have large pods and seeds for obtaining better segregants.     

Digenic nature of male sterility in pepper (Capsicum annuum L.)

Summary A cross was made between two nearly isogenic lines differing for male sterility genes, viz. ms₁ms₁Ms₂Ms₂ s Ms₁Ms₁Ms₂ms₂. F₁ plants yielded F₂ populations which segregated either in 3:1 or 9:7 ratios of fertile vs male sterile individuals. Test crosses between male sterile and male fertile sibs in the 9:7 segregating populations provided a few lines in which most of the progenies were male sterile. A 3:1 ratio model of male steriles vs fertiles is suggested and the value of the system is discussed.Contribution A.R.O. Agricultural Research Organization, The Volcani Center, Bet Dagan 50 250, Israel No. 3703-E, 1992 series.     

The probable genome donors to Arachis hypogaea L. based on arachin seed storage protein

Summary Interrelationships among six diploid species (A. chacoense, A. villosulicarpa, A. batizocoi, A. correntina, A. duranensis and A. cardenasii), tetraploid wild groundnut A. monticola and four accessions of A. hypogaea were studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of total seed proteins and arachin immunoprecipitates. Arachin in A. monticola and A. hypogaea cv. Trombay Groundnut 9 (TG-9) was composed of four acidic subunits (47.5 kd, 45.1 kd, 42.6 kd and 41.2 kd) and one major basic subunit (21.4 kd). The arachin subunit pattern in cv. Spanish Improved (SP) and TG-1 was almost similar to the pattern observed in A. monticola with the exception that the SP lacked the 41.2 kd and TG-1 lacked the 42.6 kd acidic subunits of A. monticola. Seed extracts of all diploid species studied reacted with the anti-arachin antibodies raised against SP arachin. The electrophoretic analysis of immunoprecipitates of diploid species showed a range of acidic subunits from 46.2 kd to 41.2 kd and one or two basic subunits of 21.4 kd and 20.2 kd. None of the diploid species showed the 47.5 kd subunit found in A. monticola or A. hypogaea. Of the diploid species, A. duranensis and A. cardenasii demonstrated two acidic subunits of 45.1 kd and 41.2 kd and a basic subunit of 21.4 kd as found in A. monticola. Likewise A. batizocoi showed two acidic subunits of 45.1 kd and 42.6 kd and the basic subunit of 21.4 kd as was observed in A. monticola. Based on electrophoretic data, our research supports the earlier conclusion that the probable genome donors to A. monticola are A. batizocoi and A. duranensis or A. cardenasii.     

Ribosomal DNA repeat unit polymorphism and heritability in peanut (Arachis hypogaea L.) accessions and related wild species

Repeat unit length and restriction site variation in ribosomal RNA geneclusters (rDNA) was surveyed in 77 Arachis accessions, includingsamples from 39 accessions of cultivated Arachis hypogaea(2n=4x=40), 36 accessions representing 15 related tetraploid and diploidwild species, and two synthetic amphidiploids. Total genomic DNA wasdigested with five restriction enzymes, and probed with three heterologousribosomal clones of wheat and broad bean. Four rDNA repeat unit lengthclasses were recognized in the Arachis species. Restriction site analysisshowed that some SacI, BamHI and TaqI cleavage sites in rDNA unit werehighly conserved. With few exceptions, the variable BamHI and EcoRV siteswere able to differentiate the taxonomic sections and species, respectively.Arachis hypogaea and A. duranensis accessions produced fourrDNA length classes. Among these, three were identical with those of otherArachis species. A SacI restriction site (s) from probe (Ver6-5) cangenerally distinguish the two subspecies A. hypogaea ssp. hypogaea and A. hypogaea ssp. fastigiata. Forty nine per centof bands were polymorphic across the A. hypogaea accessionsanalysed. This study does not support A. batizocoi to be a progenitorof A. hypogaea. For the gene array, the contribution from eachparental genome can be detected in the two synthetic amphidiploids.     

Genetics,genomics and breeding of groundnut (Arachis hypogaea L.)

Groundnut is an important food and oil crop in the semiarid tropics, contributing to household food consumption and cash income. In Asia and Africa, yields are low attributed to various production constraints. This review paper highlights advances in genetics, genomics and breeding to improve the productivity of groundnut. Genetic studies concerning inheritance, genetic variability and heritability, combining ability and trait correlations have provided a better understanding of the crop's genetics to develop appropriate breeding strategies for target traits. Several improved lines and sources of variability have been identified or developed for various economically important traits through conventional breeding. Significant advances have also been made in groundnut genomics including genome sequencing, marker development and genetic and trait mapping. These advances have led to a better understanding of the groundnut genome, discovery of genes/variants for traits of interest and integration of marker‐assisted breeding for selected traits. The integration of genomic tools into the breeding process accompanied with increased precision of yield trialing and phenotyping will increase the efficiency and enhance the genetic gain for release of improved groundnut varieties.     

The genomes of Arachis hypogaea. 1. Cytogenetic studies of putative genome donors

Summary Cytological studies of wild diploid Arachis species in the same section of the genus (sect. Arachis) as the cultivated peanut A. hypogaea L. show, with one exception, a karyotype characterized by the presence of 9 pairs of larger chromosomes and one pair of small (A) chromosomes. The exceptional species A. batozocoi Krap. et Greg. has a more uniform karyotype. Interspecific hybrids between diploid species of similar karyotype have moderate to high pollen stainability, those involving A. batizocoi have zero pollen stainability and a very irregular PMC meiosis. Such infertile hybrids are the most likely to produce fertile, stable amphidiploids on doubling the chromosome complement. It is suggested that the cultivated peanut could have originated from such a sterile interspecific hybrid and on morphological and phytogeographic grounds the most likely genome donors are A. cardenasii (nomen nudum) and A. batizocoi of the species within section Arachis, which have been collected up to the present time.Paper number 5560 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC 27650     

Interspecific hybridization in the genus Arachis through embryo culture

Summary The embryos of a cultivated tetraploid peanut (Arachis hypogaea), a wild diploid species (A. villosa), and their hybrid embryos, which generally abort in nature, were cultured in vitro and the plants have been successfully transferred to the soil. The hybrids showed triploid chromosome number (3x=30). The significance of wide hybridization in peanut-improvement programs is discussed.     

Variation in progenies of an Arachis hypogaea x diploid wild species hybrid

Summary Derivatives of a cross between cultivated peanuts, Arachis hypogaea L. (2n=40), and the wild species collection GKP 10017 (2n=20) were compared morphologically, for leafspot resistance and for yield. The objective of the study was to determine the effects of wild species germplasm on the A. hypogaea genome. The sterile F₁ hybrid which resulted from crossing the two species was treated with colchicine to restore fertility at the 6x ploidy level. The resulting hexaploid was cytologically unstable and progeny lost chromosomes until stability was regained at the 2n=40 chromosome level. Forty-seven characters were used to analyze the variation among plants in the tetraploid interspecific hybrid population. The plants were compared to four cultivated lines plus GKP 10017. Many hybrids were intermediate to the two parents in morphology. Individual traits such as growth habit, pod and seed size, elongation of the constricted area between pods, nodulation and leaflet size were altered by the presence of GKP 10017 germplasm in many of the hybrid plants. Cercospora arachidicola Hori and Cercosporidium personatum (Berk. & Curt.) Deighton resistances were evaluated for all plants. Several hybrids had few lesions due to either leafspot pathogen. In addition, 24 largeseeded interspecific hybrid selections were compared to the cultivated variety NC 5 for yield. Five selections were superior to both parents at p=0.01. Morphology, disease resistance and yields appeared to be greatly influenced by the wild species GKP 10017 germplasm in plants of the interspecific hybrid population. The potentials of using wild species for improvement of the cultivated peanut are discussed.Paper number 5948 of the journal series of the North Carolina Agricultural Research Service, Raleigh, NC 27650. The investigation was supported in part by ICRISAT and SEA-CR grant no. 701-15-51.     

The genomes of Arachis hypogaea 2. The implications in interspecific breeding

Summary The existence of structural differentiation between genomes in section Arachis of the genus Arachis has important implications in the utilization of diploid wild species in this section as a germplasm resource. Maximum expression of desirable characters may not be achieved unless tetrasomic dose levels can be achieved. Possible breeding strategies discussed include natural and induced gene exchange between genomes and chromosome substitution which could be brought about by manipulation of ploidy level and where appropriate the use of ionizing radiation. Such strategies could be tested in the improvement of resistance to the Cercospora leafspots.Paper number 5561 of the Journal Series of the North Carolina Agricultural Experimental Station, Raleigh, NC 27650.