Nalini Mallikarjuna

Influence of foliar chemical compounds on the development of Spodoptera litura (Fab.) in interspecific derivatives of groundnut

Abstract:  Tobacco armyworm, Spodoptera litura (Fab), a polyphagous insect, is an important pest of groundnut (Arachis hypogaea L). It is one of the insect pests which had developed resistance to insecticides. Currently there are no cultivars of groundnut which express high level of resistance to S. litura. Wild species of groundnut, which show high levels of resistance, have been identified. Arachis kempff‐mercadoi is one such wild species, which is reported to be resistant to S. litura, and indicated that in wild species three flavonoids chlorogenic acid, quercetin and rutin are involved in the components of resistance. In the present study, although these flavonoids had an effect on larval mortality, statistical analysis revealed that quercetin had a major effect due to high correlation of quercetin with chlorogenic acid and rutin. Interspecific derivatives were obtained as a result of crossing cultivated groundnut with A. kempff‐mercadoi. In vitro studies showed high percentage of neonate larval mortality when fed on the foliage of interspecific derivatives, majority of interspecific derivatives were detrimental to larval development and had considerable effect on its subsequent progeny. Resistant derivatives were found to have high levels of flavonoids and antibiosis mechanism prevented larval growth. Susceptible derivatives and the female parent, A. hypogaea have low levels of flavonoids.

Effect of high temperature on the reproductive development of chickpea genotypes under controlled environments

High temperature during the reproductive stage in chickpea (Cicer arietinum L.) is a major cause of yield loss. The objective of this research was to determine whether that variation can be explained by differences in anther and pollen development under heat stress: the effect of high temperature during the pre- and post-anthesis periods on pollen viability, pollen germination in a medium, pollen germination on the stigma, pollen tube growth and pod set in a heat-tolerant (ICCV 92944) and a heat-sensitive (ICC 5912) genotype was studied. The plants were evaluated under heat stress and non-heat stress conditions in controlled environments. High temperature stress (29/16°C to 40/25°C) was gradually applied at flowering to study pollen viability and stigma receptivity including flower production, pod set and seed number. This was compared with a non-stress treatment (27/16°C). The high temperatures reduced pod set by reducing pollen viability and pollen production per flower. The ICCV 92944 pollen was viable at 35/20°C (41% fertile) and at 40/25°C (13% fertile), whereas ICC 5912 pollen was completely sterile at 35/20°C with no in vitro germination and no germination on the stigma. However, the stigma of ICC 5912 remained receptive at 35/20°C and non-stressed pollen (27/16°C) germinated on it during reciprocal crossing. These data indicate that pollen grains were more sensitive to high temperature than the stigma in chickpea. High temperature also reduced pollen production per flower, % pollen germination, pod set and seed number.

Ovule and embryo culture to obtain hybrids from interspecific incompatible pollinations in chickpea

Many of the wild species of chickpea were not accessible to the improvement of chickpea due to cross incompatibility. In these interspecific incompatible crosses, fertilization takes place but the embryo aborts a few days later. The only way to obtain hybrid plants is by the application of growth regulators to pollinated pistils to prevent initial pod abscission and to save the aborting hybrid embryos by embryo rescue techniques. Although there are a few papers on regeneration from different explants of chickpea, information on embryo rescue techniques is not available. The paper summarises the embryo rescue techniques developed for chickpea, by the use of which hybrid plants between C. arietinum and C. pinnatifidum were produced. The paper also emphasises the effect of genotype to successfully obtain hybrids. The morphology of the hybrid plants resembled the male parent in leaf structure and growth habit. The colour of the flowers produced on the hybrid plant was pale violet, resembling the male parent whose flowers were violet in colour. The flower colour of the female parent was white.

Advances in genetics and molecular breeding of three legume crops of semi-arid tropics using next-generation sequencing and high-throughput genotyping technologies.

Molecular markers are the most powerful genomic tools to increase the efficiency and precision of breeding practices for crop improvement. Progress in the development of genomic resources in the leading legume crops of the semi-arid tropics (SAT), namely, chickpea (Cicer arietinum), pigeonpea (Cajanus cajan) and groundnut (Arachis hypogaea), as compared to other crop species like cereals, has been very slow. With the advances in next-generation sequencing (NGS) and high-throughput (HTP) genotyping methods, there is a shift in development of genomic resources including molecular markers in these crops. For instance, 2,000 to 3,000 novel simple sequence repeats (SSR) markers have been developed each for chickpea, pigeonpea and groundnut. Based on Sanger, 454/FLX and Illumina transcript reads, transcriptome assemblies have been developed for chickpea (44,845 transcript assembly contigs, or TACs) and pigeonpea (21,434 TACs). Illumina sequencing of some parental genotypes of mapping populations has resulted in the development of 120 million reads for chickpea and 128.9 million reads for pigeonpea. Alignment of these Illumina reads with respective transcriptome assemblies have provided >10,000 SNPs each in chickpea and pigeonpea. A variety of SNP genotyping platforms including GoldenGate, VeraCode and Competitive Allele Specific PCR (KASPar) assays have been developed in chickpea and pigeonpea. By using above resources, the first-generation or comprehensive genetic maps have been developed in the three legume species mentioned above. Analysis of phenotyping data together with genotyping data has provided candidate markers for drought-tolerance-related root traits in chickpea, resistance to foliar diseases in groundnut and sterility mosaic disease (SMD) and fertility restoration in pigeonpea. Together with these trait-associated markers along with those already available, molecular breeding programmes have been initiated for enhancing drought tolerance, resistance to fusarium wilt and ascochyta blight in chickpea and resistance to foliar diseases in groundnut. These trait-associated robust markers along with other genomic resources including genetic maps and genomic resources will certainly accelerate crop improvement programmes in the SAT legumes.

Toward doubled haploid production in the Fabaceae: progress, constraints, and opportunities

The Fabaceae species have a major role to play in sustainable farming systems, but they have lagged behind other families in respect to the development of doubled haploid protocols for plant improvement. Currently, no plant improvement program uses doubled haploids on a routine basis for any member of the Fabaceae. There has recently been renewed interest in haploid research as the usefulness of doubled haploid material in molecular mapping has become clear. This review provides a comprehensive account of the current information regarding the development of haploid protocols in the Fabaceae. In the Fabaceae crop species there have been isolated reports of haploid plant induction in the phaseoloid clade; soybean, cowpea and pigeonpea, as well as promising progress towards haploidy in peanut and winged bean. As yet there have been no reports of haploid plant production in the galegoid clade, but early stage haploid embryogenesis has been achieved in chickpea, field pea, and lupin. Success in the production of haploid plants has also been reported within the pasture genera Lotus, Medicago, and Trifolium and the arboreal genera Cassia, Peltophorum, and Albizzia. A review of the literature has enabled us to identify some general similarities between the protocols developed for haploid plant induction across the various legumes. These are the culture of intact anthers; use of a cold pretreatment to induce sporophytic development; targeting of microspores at the uninucleate stage of development; and use of MS (Murashige and Skoog, 1962) based nutrient medium with plant growth regulators to encourage continued division following induction. These protocol commonalities will assist researchers to identify approaches suited to their target Fabaceae species. The paucity of research funding for haploid research in most Fabaceae species has highlighted the need for strong collaborative linkages between institutions and researchers. Referees: Professor Laima Kott, Crop Science Department, University of Guelph, Guelph ON N1G 2W1.

Production of hybrids between Cajanus platycarpus and Cajanus cajan

SummaryCajanus platycarpus a wild species of pigeonpea incompatible with the cultigen has many desirable characters important for the improvement of cultivated pigeonpea. In the present study, barriers to hybridization were studied and were identified as post-zygotic. Efficient embryo rescue techniques were developed. As a result, hybrids were produced. Morphological and cytological studies as well as esterase isozyme band pattern confirmed the hybrid nature of the plants. The F1 hybrids were completely pollen sterile. Meiotic studies were carried out to check for the cause of pollen sterility.

Development of new sources of tetraploid Arachis to broaden the genetic base of cultivated groundnut (Arachis hypogaea L.)

Groundnut, an important crop of many countries of the world, is susceptible to a range of diseases and pests. High levels of resistances are not available in the cultivated gene pool as the crop is said to have a narrow genetic base. Narrow genetic base is attributed to the evolution of the crop which took place by the combination of A and B genome species, and later doubling their chromosome number, giving rise to tetraploid cultivated groundnut. Direct utilization of cross-compatible wild relatives, which are diploids, to broaden the genetic base and introduction of useful traits, is not a straight-forward process due to ploidy differences between the cultivated species and wild relatives. Hence amphiploids and autotetraploids were created by not only combining the putative genomes, but many other A and B genome species, thus producing a highly variable population of tetraploid groundnuts also called new sources of Arachis hypogaea. This study describes the development and characterization of newly generated tetraploid groundnuts and the level of molecular diversity as assessed by DArT markers.

Introgression of Cajanus platycarpus genome into cultivated pigeonpea, C. cajan

SummaryCajanus platycarpus, an incompatible wild species from the tertiary gene pool of pigeonpea (C. cajan (L.) Millspaugh), has many desirable characteristics for the improvement of cultivated varieties. To necessitate such transfers, embryo rescue techniques were used to obtain F1 hybrids. The F1 hybrids were treated with colchicine to obtain tetraploid hybrids, that were selfed to obtain F2, F3 and F4 progenies. All of the hybrids and subsequent progenies had an intermediate morphology between the two parents. Backcrossing of the tetraploid hybrids with cultivated pigeonpea was not possible given embryo abortion, with smaller aborted embryos than those obtained in the F0 parental cross.As a route of introgression, diploid F1 hybrids were backcrossed with cultivated pigeonpea and BC1 progeny obtained by in vitro culture of aborting embryos. BC2 plants were obtained by normal, mature seed germination. Although embryo rescue techniques had to be used to obtain F1 and BC1 plants, it was possible to produce BC2 and subsequent generations through direct mature seed. Every backcross to cultivated pigeonpea increased pollen fertility and the formation of mature seeds.

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.

Production of hybrids between Cajanus acutifolius and C. cajan

There are many wild species of pigeonpea which are endemic to Australia. These wild species are cross incompatible with cultivated species of Indian origin. Cajanus acutifolius is one such species which does not easily cross with cultivated pigeonpea. Interspecific pollinations lead to hybrid seeds which were semi-shrivelled. Very few seeds germinated to give rise to F1 plants. Backcrossing the hybrid plants to C. cajan, the male parent, gave rise to aborting seeds which did not germinate in vivo hence BC1 plants are obtained after saving the aborting embryos in vitro. BC1 plants showed normal meiotic pairing, but had low pollen fertility. The reasons for embryo abortion and low pollen fertility in spite of normal meiosis could be due to the effect of wild species cytoplasm.