Cultivated Pigeonpea Research Articles

Phylogenetic analysis of pigeonpea (<i>Cajanus cajan</i>) genotypes using <i>Panzee </i>retrotransposon based SSAP markers

In the present study, twenty one pigeonpea [Cajanus cajan (L.) Millspaugh] genotypes representing three different gene pools were analysed for phylogenetic relationships using sequence specific amplification polymorphism markers. Four primers were screened involving selective AFLP primers in combination with primer specific to 5'LTR region of Panzee retrotransposon. A total of 183 bands were scored, out of which 166 (90.71%) bands were polymorphic with an average of 41.5 polymorphic bands per primer combination. Polymorphism information content (PIC) values ranged from 0.15 [Panzee-LTR/ EcoRI (+AAC)] to 0.26 [Panzee-LTR/ EcoRI (+AAG)] for four primer combinations. Resolving power (RP) values ranged from 10.14 [Panzee-LTR/ EcoRI (+AAC)] to 24.92 [Panzee-LTR/ MseI (+CAC)], whereas marker index (MI) values ranged from 5.25 [Panzee-LTR/ EcoRI (+AAC)] to 14.25 [Panzee-LTR/ MseI (+CAC)] exhibiting positive correlation (r2=0.99 P<0.05). Primer Panzee-LTR/ MseI (+CAC) with higher values of RP (24.92) and MI (14.25) was found most informative for analysing the phylogenetic relationships. NJ tree based on 166 polymorphic SSAP markers exhibited concordant relationships among pigeonpea genotypes supported by high bootstrap values. The genotypes belonging to tertiary gene pools and primary gene pool were placed at extremes, whereas one accession of C. cajanifolius (ICP 15632) was placed closer to primary gene pool, confirming C. cajanifolius is the closest progenitor of cultivated pigeonpea. SSAP markers produced high rate of polymorphism and revealed phylogenetic relationships among pigeonpea genotypes.

Elucidation of Genetic Relationships in the Genus Cajanus Using Random Amplified Polymorphic DNA Marker Analysis

In this present investigation, a total of 27 RAPD primers were used to elucidate the genetic relationships between cultivated Cajanus cajan cultivars and 10 allied species of primary, secondary and tertiary gene pool, including C. cajanifolius, C. scarabaeoides, C. platycarpus, C. albicans, C. volubilis, C. sericeus, C. acutifolius, C. lineatus, C. lanceolatus and C. reticulates. All primers showed polymorphism at species level and produced 215 unequivocal polymorphic bands, with an average of 7.96 bands per primer. These polymorphic primers exhibited variation with regard to average band informativeness, resolving power, and showed high polymorphism information content value. No single primer was able to distinguish between all the two cultivars of C. cajan and ten allied species of Cajanus, but several species specific amplified fragments were observed. The pair wise Jaccard’s similarity coefficient values revealed high level of inter-specific genetic variation in the genus Cajanus. Cluster analysis exhibited the grouping of two C. cajan accessions with C. cajanifolius in one cluster, while except C. platycarpus, all the nine wild Cajanus species belonging to the secondary and tertiary gene pool form another cluster. The present analysis more or less agreed with the sectional classification of the genus Cajanus, and it has been hypothesized that cultivated pigeonpea has evolved through multi-genomic interaction through C. cajanifolius, and it has experienced minor genomic reorganization during its divergence. Again, identification of species specific amplification pattern substantiated the utility of RAPD markers on selection of suitable species to transfer the desirable trait into cultivated C. cajan, through marker aided breeding for its genetic augmentation, and also for the effective management of genetic resources of C. cajan.

Genetic Patterns of Domestication in Pigeonpea (Cajanus cajan (L.) Millsp.) and Wild Cajanus Relatives

Pigeonpea (Cajanus cajan) is an annual or short-lived perennial food legume of acute regional importance, providing significant protein to the human diet in less developed regions of Asia and Africa. Due to its narrow genetic base, pigeonpea improvement is increasingly reliant on introgression of valuable traits from wild forms, a practice that would benefit from knowledge of its domestication history and relationships to wild species. Here we use 752 single nucleotide polymorphisms (SNPs) derived from 670 low copy orthologous genes to clarify the evolutionary history of pigeonpea (79 accessions) and its wild relatives (31 accessions). We identified three well-supported lineages that are geographically clustered and congruent with previous nuclear and plastid sequence-based phylogenies. Among all species analyzed Cajanus cajanifolius is the most probable progenitor of cultivated pigeonpea. Multiple lines of evidence suggest recent gene flow between cultivated and non-cultivated forms, as well as historical gene flow between diverged but sympatric species. Evidence supports that primary domestication occurred in India, with a second and more recent nested population bottleneck focused in tropical regions that is the likely consequence of pigeonpea breeding. We find abundant allelic variation and genetic diversity among the wild relatives, with the exception of wild species from Australia for which we report a third bottleneck unrelated to domestication within India. Domesticated C. cajan possess 75% less allelic diversity than the progenitor clade of wild Indian species, indicating a severe “domestication bottleneck” during pigeonpea domestication.

Pod surface exudates of wild relatives of pigeonpea influence the feeding preference of the pod borer, Helicoverpa armigera

Wild relatives of crops are an important source of resistance genes against insect pests. However, it is important to identify the accessions of wild relatives of crops with different mechanisms of resistance to broaden the basis and increase the levels of resistance to insect pests. Therefore, we studied the feeding behavior of pod borer, Helicoverpa armigera, which is the most damaging pest of pigeonpea, in relation to biochemical characteristics of the pod surface exudates in a diverse array of germplasm accessions belonging to 12 species of pigeonpea wild relatives. Feeding by H. armigera larvae was significantly lower on the unwashed or water-, methanol-, or hexane-washed pods of Canajus sericeus, C. scarabaeoides, Flemingia bracteata, F. stricta, and Rhynchosia aurea than those of C. acutifolius, C. albicans, C. cajanifolius, C. lineatus, D. ferruginea, P. scariosa, R. bracteata, and the cultivated pigeonpea, C. cajan genotypes, ICPL 87, and ICPL 332, although there were a few exceptions. The methanol-washed pods of wild relatives were less preferred for feeding by the H. armigera larvae than the unwashed pods, but the hexane-washed pods were preferred more than the unwashed pods. The results suggested that methanol extracted the phagostimulants from the pod surface, while hexane removed the antifeedants. The high-performance liquid chromatography (HPLC) finger printing of methanol and hexane pod surface extracts showed qualitative and quantitative differences in compounds present on the pod surface of different wild relatives of pigeonpea. Some of the peaks in HPLC profiles were associated with feeding preference of the third-instar larvae of H. armigera. There was considerable diversity in wild relatives of pigeonpea as revealed by principal component analysis based on HPLC fingerprints of pod surface extracts in methanol and hexane, and H. armigera feeding on the pods. Wild pigeonpea accessions with low amounts of phagostimulants and high amounts of antifeedants may be used for introgression of resistance genes into the cultivated pigeonpea to develop varieties with broad-based resistance to H. armigera. There is considerable diversity among the wild relatives of pigeonpea, and the accessions with resistance to pod borer. These can be used to broaden the basis and increase the levels of resistance to H. armigera.

Protease Inhibitors in Wild Relatives of Pigeonpea against the Cotton Bollworm/Legume Pod Borer, <i>Helicoverpa armigera</i>

Cotton bollworm/legume pod borer, Helicoverpa armigera is one of the most damaging pests worldwide. Be-cause of the difficulties associated with chemical control of this pest, emphasis has been placed on developing transgenic plants with resistance to H. armigera. Since toxin genes from the bacterium, Bacillus thuringien-sis (Bt) have been deployed on a large scale, there is need to scout for alternate genes which could be deployed alone or in combination with the Bt genes for pest management. Therefore, we evaluated the wild relatives of pigeonpea, which have shown high levels of resistance to this pest, for the protease inhibitors (PIs) under in vivo and in vitro inhibitions. Accessions belonging to Cajanus albicans, C. cajanifolius, C. sericeus, Flemingia bracteata, and Rhynchosia bracteata showed complete inhibition of H. armigera gut proteinases (HaGPs). Some of the C. scarabaeoides accessions (ICPW 116, 152, 278 and 280) exhibited partial inhibition at low concentrations of the PIs. All accessions of wild relatives of pigeonpea showed high to moderate level of inhibition at pH 7.8. Cultivated pigeonpea, ICPL 87 exhibited monomorphism in terms of trypsin inhibitor (TI) and chymotrypsin inhibitor (CTI) isoforms, contrary to the diverse inhibitory profiles of wild pigeonpeas. Cajanus albicans, C. platycarpus, C. scarabaeoides, and R. bracteata showed more number of TI and CTI bands than the cultivated pigeonpea. Protease inhibitor isoforms of wild relatives of pigeonpea showed significant variation in number, band pattern, and protein specificities towards trypsin, chymotrypsin, and H. armigera gut proteinases (HaGPs) as compared to the cultivated pigeonpea. The PIs from the wild relatives of pigeonpea showed considerable potential against the HaGPs, and could be considered as potential candidates for use in genetic transformation of crops for pest management, including H. armigera.

Ensuring Genetic Purity of Pigeonpea Hybrids by Incorporating a Naked‐Eye Polymorphic Marker in A and B Lines

ABSTRACTTo enhance the productivity of pigeonpea [Cajanus cajan (L.) Millspaugh] a hybrid breeding technology, based on the cytoplasmic nuclear male‐sterility (CMS) system and partial natural outcrossing, is currently been used. However, there are difficulties to maintain genetic purity of the hybrids and their parents. The incorporation of an easily identifiable morphological marker (naked eye polymorphism [NEP]) could be used to determine seed purity. The morphological marker selected for this study, obcordate leaf, is not present in cultivated pigeonpea; it is inherited as a single recessive gene and can be observed soon after planting (approx. 6 wk). To incorporate the obcordate leaf shape into hybrid parents, the trait was transferred from the germplasm accession ICP 5529 into male‐sterile (A lines) and the corresponding maintainers (B lines). The hybrids derived from crosses involving obcordate leaf A lines and normal leaf fertility restorers (R lines) were fully fertile and had normal lanceolate leaves; thus the difference between A line and hybrids was clear. The use of obcordate leaf as a NEP marker in pigeonpea would contribute to preserve parental line purity and confirm hybrid status.

Diversity and geographical gaps inCajanus scarabaeoides(L.) Thou. germplasm conserved at the ICRISAT genebank

Crop wild relatives are important components of agro-ecosystems as potential gene contributors for crop improvement programmes.Cajanus scarabaeoides(L.) Thou., a pigeonpea wild relative is crossable with cultivated pigeonpea and possesses several beneficial traits. Hundred accessions conserved at the ICRISAT genebank were characterized for 13 quantitative and ten qualitative traits to assess the diversity in the collection. Highly significant genotypic variance for leaflet length, days to 5% maturity, seeds per pod, 100-seed weight, seed protein content and trichome density and length was observed. AllC. scarabaeoidesaccessions used in the present study are the best sources for extra early ( < 80 d to 50% flowering) and early maturity (80–100 d to 50% flowering). Eight accessions (ICP 15692, ICP 15696, ICP 15698, ICP 15699, ICP 15712, ICP 15719, ICP 15732 and ICP 15758) and the control ICP 15695 have produced more than 92% healthy pods per plant and higher number of seed per pod (4–6 seeds). Accessions in cluster 2, 3 and 4 with low mean values for days to 50% flowering were found as the best sources for early flowering and maturity. Accessions in cluster 2 and 3 for seeds per pod and cluster 2 for healthy pods per plant were found as promising sources for use in crop improvement. Mean diversity over all clusters was highest (H= 0.57 ± 0.01) for seeds per pod and lowest for days to 50% flowering (0.48 ± 0.02). Significant negative correlation between pods per raceme and healthy pods per plant ( − 0.213) indicated high pod damage in racemes having more pods. Trichome length had highly significant negative association with healthy pods per plant ( − 0.293). The probability map generated using FloraMap, a GIS tool, revealed the occurrence ofC. scarabaeoidesquite close to the origin and dispersal of pigeonpea. The probability (>75%) map identified a total of 118 provinces covering 790 districts in Bangladesh, Cambodia, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Papua New Guinea, Philippines, Thailand and Vietnam as geographical gaps in the collection. Complete passport data including location coordinates should be collected while collecting the germplasm to analyze the spatial aspects of species distribution.

Amplification of chickpea‐specific SSR primers in Cajanus species and their validity in diversity analysis

With 2 figures and 3 tables AbstractPaucity of polymorphic molecular markers in pigeonpea, Cajanus cajan (L.) Millsp., has been a major limiting factor in application of molecular tools for its genetic improvement. As the development of microsatellite markers requires considerable time, expertise and research infrastructure, transfer of markers from other related genera offers an alternative option to increase the number of available markers. Since microsatellite sequences are conserved across Fabaceae taxa, transferability of 100 chickpea (Cicer arietinum L.)‐specific SSR markers was studied in two genotypes each of five wild and one cultivated species of Cajanus. The results revealed a significant transferability (46%) of chickpea microsatellites to Cajanus. In cultivated pigeonpea, chickpea‐specific SSRs showed 38–39% transferability, while among wild Cajanus species, it ranged from 26% in Cajanus sericeus ICP 15760 to 40% in C. sericeus ICP 15761. The transferable primers exhibited extensive polymorphism in Cajanus with an average number of 4.11 alleles per marker. High level of polymorphism exhibited by chickpea microsatellite markers in the present study indicates their usefulness in diversity analysis, mapping agronomically important traits and marker‐assisted breeding in pigeonpea.

Novel SSR Markers for Polymorphism Detection in Pigeonpea (Cajanus spp.)

With 1 figure and 4 tables AbstractWith an objective to expand the repertoire of molecular markers in pigeonpea (Cajanus cajan), 36 microsatellite or simple sequence repeat (SSR) loci were isolated from a SSR‐enriched genomic library. Primer pairs were designed for 23 SSR loci, of which 16 yielded amplicons of expected size. Thirteen SSR markers were polymorphic amongst 32 cultivated and eight wild pigeonpea genotypes representing six Cajanus species. These markers amplified a total of 72 alleles ranging from two to eight alleles with an average of 5.5 alleles per locus. The polymorphic information content for these markers ranged from 0.05 to 0.55 with an average of 0.32 per marker. Phenetic analysis clearly distinguished all wild species genotypes from each other and from the cultivated pigeonpea genotypes. These markers should be useful for genome mapping, trait mapping, diversity studies and assessment of gene flow between populations in pigeonpea.

New microsatellite markers for pigeonpea (cajanus cajan (L.) millsp.)

BackgroundPigeonpea is a nutritious tropical legume with several desirable characteristics but has been relatively neglected in terms of research. More efficient improvement can be achieved in this crop through molecular breeding but adequate molecular markers are lacking and no linkage map has been developed so far. Microsatellites remain the markers of choice due to their high polymorphism and their transferability from closely related genera. The overall objective of this study was to develop microsatellite markers from an enriched library of pigeonpea as well as testing the transferability of soybean microsatellites in pigeonpea.ResultsPrimers were designed for 113 pigeonpea genomic SSRs, 73 of which amplified interpretable bands. Thirty-five of the primers revealed polymorphism among 24 pigeonpea breeding lines. The number of alleles detected ranged from 2 to 6 with a total of 110 alleles and an average of 3.1 alleles per locus. GT/CA and GAA class of repeats were the most abundant di-nucleotide and tri-nucleotide repeats respectively. Additionally, 220 soybean primers were tested in pigeonpea, 39 of which amplified interpretable bands.ConclusionDespite the observed morphological diversity, there is little genetic diversity within cultivated pigeonpea as revealed by the developed microsatellites. Although some of the tested soybean microsatellites may be transferable to pigeonpea, lack of useful polymorphism may hinder their full use. A robust set of markers will still have to be developed for pigeonpea genome if molecular breeding is to be achieved.

Influence of pod maturity and level of domestication on biochemical components in wild and cultivated pigeonpea (Cajanus cajan)

AbstractVariations in the trypsin inhibitors and lectin content in the developing pods of thirty accessions of Cajanus scarabaeoides, a wild relative of pigeonpea, from wide geographical locations and six cultivated genotypes were estimated at juvenile, immature and mature stages of pod development. Genotypes differed at all three stages for these two biochemical components. Total protein and trypsin inhibitor contents were higher in the wild accessions than in the cultivated genotypes. Although lectin content in the juvenile stage of pod development in the wild accessions ICPW 138 and ICPW 98 was highest, it was absent in the mature pods in both the cultivated and the wild genotypes. Very high broad‐sense heritability estimates indicated the possibility of involvement of few genes in the inheritance of these biochemical components, which could be easily introgressed into the elite agronomic background.

Genomic relationships among 11 species in the genus Cajanus as revealed by seed protein (albumin and globulin) polymorphisms

SDS-PAGE analysis of seed albumins and globulins from two pigeonpea, Cajanus cajan, cultivars (DSLR-17 and BDN-2) and ten wild species, including C. cajanifolius, C. lineatus, C. sericeus, C. acutifolius, C. lanceolatus, C. reticulates, C. albicans, C. scarabaeoides, C. volubilis and C. platycarpus, resulted in 34 albumin and 27 globulin polypeptides. Proximity matrix analysis based on electrophoretic banding patterns of albumins and globulins jointly revealed C. cajanifolius to be closest to C. cajan having similarity coefficients of 0.595 and 0.676, respectively. Cluster analysis also exhibited the grouping of C. cajanifolius with C. cajan in one cluster. C. platycarpus has been out grouped. The present analysis more or less agreed with the sectional classification of the genus Cajanus and it has been hypothesized that cultivated pigeonpea has evolved through multi-genomic interaction involving C. cajanifolius and that it has experienced minor genomic reorganization during its divergence.

Low level of genetic diversity in cultivated Pigeonpea compared to its wild relatives is revealed by diversity arrays technology

Understanding the distribution of genetic diversity among individuals, populations and gene pools is crucial for the efficient management of germplasm collections and breeding programs. Diversity analysis is routinely carried out using sequencing of selected gene(s) or molecular marker technologies. Here we report on the development of Diversity Arrays Technology (DArT) for pigeonpea (Cajanus cajan) and its wild relatives. DArT tests thousands of genomic loci for polymorphism and provides the binary scores for hundreds of markers in a single hybridization-based assay. We tested eight complexity reduction methods using various combinations of restriction enzymes and selected PstI/HaeIII genomic representation with the largest frequency of polymorphic clones (19.8%) to produce genotyping arrays. The performance of the PstI/HaeIII array was evaluated by typing 96 accessions representing nearly 20 species of Cajanus. A total of nearly 700 markers were identified with the average call rate of 96.0% and the scoring reproducibility of 99.7%. DArT markers revealed genetic relationships among the accessions consistent with the available information and systematic classification. Most of the diversity was among the wild relatives of pigeonpea or between the wild species and the cultivated C. cajan. Only 64 markers were polymorphic among the cultivated accessions. Such narrow genetic base is likely to represent a serious impediment to breeding progress in pigeonpea. Our study shows that DArT can be effectively applied in molecular systematics and biodiversity studies.

AFLP Fingerprinting in Pigeonpea (Cajanus cajan (L.) Millsp.) and its Wild Relatives

Detection of DNA polymorphism in cultivated pigeonpea (Cajanus cajan) and two of its wild relatives Cajanus volubilis and Rhynchosia bracteata is reported here for the first time using amplified fragment length polymorphism (AFLP) fingerprinting. For this purpose, two EcoRI (three selective nucleotides) and 14 MseI (three selective nucleotides) primers were used. The two wild species shared only 7.15% bands with the pigeonpea cultivars, whereas 86.71% common bands were seen among cultivars. Similarly, 62.08% bands were polymorphic between C. volubilis and pigeonpea cultivars in comparison to 63.33% polymorphic bands between R. bracteata and pigeonpea cultivars, and 13.28% polymorphic bands among pigeonpea cultivars. The cluster analysis revealed low polymorphism among pigeonpea cultivars and very high polymorphism between cultivated pigeonpea and its wild relatives. The AFLP analysis also indicated that only one primer combination (EcoRI + ACT and MseI + CTG), at the most any four primer pair combinations, are sufficient for obtaining reliable estimation of genetic diversity in closely related cultivars like pigeonpea material analyzed herein. AFLP analysis may prove to be a useful tool for molecular characterization of pigeonpea cultivars and its wild relatives and for possible use in genome mapping.

Susceptibility of pigeonpea and some of its wild relatives to predation by Helicoverpa armigera: implications for breeding resistant cultivars

Helicoverpa armigera (Hübner), the podborer, is a pest of considerable economic importance to crop production across Asia and Australia. The larvae cause significant damage to many crops including the cultivated pigeonpea, Cajanus cajan. We have conducted oviposition and pod feeding-damage studies with H. armigera on 5 varieties of C. cajan, 6 other Cajanus species, and Rhynchosia bracteata. The species could be divided into podborer-resistant [C. scarabaeoides (ICPW 83), C. cajanifolius, C. sericeus, C. albicans, and C. platycarpus], moderately resistant [Rhynchosia bracteata and some varieties of C. cajan], or susceptible [C. cajan (ICPL 87)]. At 100 μg/g a methanol extract of the susceptible cultivar of Cajanus (ICPL 87) stimulated significantly more oviposition than a similar extract of the resistant species C. scarabaeoides, ICPW 83. Pod surface extracts of both ICPW 83 and ICPL 87 contained isoquercitrin, quercetin, and quercetin-3-methyl ether, although they were present at much lower concentrations in ICPW 83. A fourth compound, 3-hydroxy-4-prenyl-5-methoxystilbene-2-carboxylic acid (stilbene), was detected in a methanol extract of the pod surfaces of ICPL 87. A methanol extract of ICPL 87, from which the stilbene had been removed, stimulated oviposition when paired with the whole extract. These results are discussed in relation to the selection of varieties with morphological and chemical characters that can be used for developing cultivars less susceptible to podborer.

Inheritance of trichomes and resistance to pod borer (Helicoverpa armigera) and their association in interspecific crosses between cultivated pigeonpea (Cajanus cajan) and its wild relative C. scarabaeoides

The legume pod borer, Helicoverpa armigera, is one of the most devastating pests of pigeonpea. High levels of resistance to pod borer have been reported in the wild relative of pigeonpea, Cajanus scarabaeoides. Trichomes (their type, orientation, density and length) and their exudates on pod wall surface play an important role in the ovipositional behavior and host selection process of insect herbivores. They have been widely exploited as an insect defense mechanism in number of crops. In the present investigation, inheritance of resistance to pod borer and different types of trichomes (A, B, C and D) on the pod wall surface in the parents (C. cajan and C. scarabaeoides) and their F1, F2, BC1 (C. cajan × F1), and F3 generations has been studied. Trichomes of the wild parents (high density of the non-glandular trichomes C and D, and glandular trichome B and low density of glandular trichome A) were dominant over the trichome features of C. cajan. A single dominant gene as indicated by the segregation patterns individually will govern each trait in the F2 and backcross generation. Segregation ratio of 3 (resistant): 1 (susceptible) for resistance to pod borer in the F2 generation under field conditions was corroborated with a ratio of 1:1 in the backcross generation, and the ratio of 1 non-segregating (resistant): 2 segregating (3 resistant: 1 susceptible): 1 non-segregating (susceptible) in F3 generation. Similar results were obtained for pod borer resistance under no-choice conditions. Resistance to pod borer and trichomes associated with it (low density of type A trichome and high density of type C) are governed individually by a dominant allele of a single gene in C. scarabaeoides. Following backcrossing, these traits can be transferred from C. scarabaeoides into the cultivated background.

Broad‐based resistance to pigeonpea sterility mosaic disease in wild relatives of pigeonpea (Cajanus: Phaseoleae)

SummarySterility mosaic disease (SMD), an important biotic constraint on pigeonpea (Cajanus cajan) in the Indian subcontinent, is caused by Pigeonpea sterility mosaic virus (PPSMV) transmitted by the eriophyid mite, Aceria cajani. Distinct PPSMV isolates occur in different geographical regions and broad‐based resistance to all these isolates is scarce in cultivated pigeonpea germplasm. Wild relatives of pigeonpea, which are known to possess resistance to several pests and diseases, were evaluated for broad‐based SMD resistance. One hundred and fifteen wild Cajanus accessions from six species (C. albicans, C. platycarpus, C. cajanifolius, C. lineatus, C. scarabaeoides and C. sericeus) were evaluated against three PPSMV isolates prevailing in peninsular India. Evaluations were done under greenhouse conditions in endemic locations of each isolate through mite‐mediated virus inoculation. Fifteen accessions showed resistance to all three isolates: ICP 15614, 15615, 15626, 15684, 15688, 15700, 15701, 15725, 15734, 15736, 15737, 15740, 15924, 15925 and 15926. Most of the wild accessions did not support mite multiplication. The majority of the accessions resistant to PPSMV following inoculations with viruliferous mites were susceptible by graft inoculation, suggesting that vector resistance is conferring resistance to infection with PPSMV. The 15 accessions identified as being resistant to infection to all three virus isolates tested are cross compatible with pigeonpea by traditional breeding. They are therefore useful for exploitation in breeding programmes to increase both the level of SMD resistance and to diversify its genetic base in the cultivated pigeonpea gene pool.

A new cytoplasmic nuclear male-sterility system derived from cultivated pigeonpea cytoplasm

Cytoplasmic male-sterility (CMS) in pigeonpea has been reported when some wild relatives of pigeonpea were crossed as the female parent with cultivated types as the male parent. In this paper we report a new source of CMS developed by using the cultivated pigeonpea as the female parent and one of its wild relative Cajanus acutifolius as the pollen donor. This is the first report in pigeonpea where CMS has been developed using the cytoplasm of cultivated pigeonpea. Several pure line cultivars of pigeonpea restored pollen fertility whereas cv. HPL 24 partially maintained male-sterility. The wild species C. acutifolius used as one of the parents, maintained complete sterility. Cytological analysis revealed that both in male-sterile as well as the fertile floral buds, meiosis proceeded normally till the tetrad stage. However in the male-sterile genotypes during the formation of tetrads, the pollen mother cell (PMC) wall did not dissolve to release the tetrads unlike in the fertile genotypes and this major event was found to be responsible for male-sterility.

Can larvae of the pod-borer, Helicoverpa armigera (Lepidoptera: Noctuidae), select between wild and cultivated pigeonpea Cajanus sp. (Fabaceae)?

Experiments were conducted to observe the feeding and food selection-behaviour of different instars of the pod-borer Helicoverpa armigera (Hübner) in response to choices between the cultivated and a wild species of Cajanus. First and second instars fed upon a cultivated variety of Cajanus cajan in preference to a wild species, C. scarabaeoides and on flowers of C. cajan, rather than pods or leaves of C. cajan. First and second instars preferred pods of C. scarabaeoides with trichomes removed to pods with trichomes present. All instars fed upon pods of C. cajan rather than those of C. scarabaeoides. Solvent extraction of the pod surfaces affected the feeding of larvae, in some instances. They preferred the unextracted pods of C. cajan; the extracted pod of C. scarabaeoides (first and second instars) or the unextracted pod of C. scarabaeoides (fourth and fifth instars). Glass-fibre disc bioassays showed that the methanol, hexane and water extracts from the pod-surface of C. cajan stimulated the feeding of fifth instars. The experiments have shown that characteristics of C. cajan, such as either the compounds present or the type and distribution of trichomes on the plant surfaces, can determine the susceptibility of C. cajan to pod-borer larvae.

Genetic variation in acquisition, and utilization of phosphorus from iron-bound phosphorus in pigeonpea

In earlier experiments it was observed that pigeonpea is one of the few crop species that can utilize fixed forms of soil-P, particularly iron-bound P (Fe-P). The present investigation was aimed at assessing the genotypic variation in P uptake from Fe-P in pigeonpea. Fifteen pigeonpea germplasm lines that comprised genotypes of different maturity groups and three wild relatives were grown in vermiculite supplied with 15 mg P either as Fe-P or Ca-P for 60 d. Significant genetic variation in P uptake from Fe-P was observed; also P-use efficiency varied substantially among the genotypes. Dry matter production was positively correlated with P uptake both under Fe-P and Ca-P treatments (r=0.78**; r=0.63*; n=15). There was no significant relation between P-use efficiency and dry matter production. Wild related species did not show higher P uptake from Fe-P than the cultivated pigeonpea. From Fe-P, the P uptake was only 36% of that from Ca-P. The best genotypes in the present study took up an amount of P equivalent to 55% of that from Ca-P. Significant differences were detected in P-uptake efficiency (μg P mg−1 root d.wt.) among the genotypes, but P uptake efficiency did not correlate with total P uptake. A positive correlation was found between P uptake and root dry matter production under Ca-P and Fe-P treatments (r=0.78**; r=0.63*; n=15). The differential P uptake by ICPL 88039, C 11, ICPL 88032, and ICPL 87 from Fe-P in the vermiculite study was confirmed in soil culture where the soil contained a small amount of available P, but substantial amounts of AI- and Fe-P. The results demonstrated the presence of a significant genotypic variation in P uptake from Fe-P in pigeonpea.