Pigeonpea Hybrids Research Articles

Unravelling the epigenomic interactions between parental inbreds resulting in an altered hybrid methylome in pigeonpea.

DNA methylation is an important heritable landmark conferring epigenetic changes in hybrids and has fascinated biologists and plant-breeders over the years. Although epigenetic changes have been documented in rice and maize hybrids, such investigations have not been reported in pigeonpea. Here, we report genome-wide methylation profiles of pigeonpea sterile and fertile inbred lines and their fertile F1 hybrid at single base resolution. We found that pigeonpea genome is relatively enriched in CG methylation. Identification of differentially methylated regions (DMRs) in the sterile and fertile parent revealed remarkable differences between their methylation patterns. Investigation of methylation status of parental DMRs in hybrid revealed non-additive methylation patterns resulting from trans-chromosomal methylation and trans-chromosomal demethylation events. Furthermore, we discovered several DMRs negatively associated with gene expression in the hybrid and fertile parent. Interestingly, many of those DMRs belonged to transposable elements and genes encoding pentatricopeptide repeats associated proteins, which may mediate a role in modulating the genes impacting pollen fertility. Overall, our findings provide an understanding of two parental epigenomes interacting to give rise to an altered methylome in pigeonpea hybrids, from genome-wide point of view.

Maternal inheritance of male sterility in the progeny of a natural hybrid between Cajanus lineatus and C. cajan

AbstractAdoption of pigeonpea hybrids in central and southern India is showing high impact with on‐farm yield advantages of >30%. The hybrid pigeonpea technology, the first in any legume crop, is based on a cytoplasmic‐nuclear male‐sterility (CMS) system. For a long‐term sustainability of hybrid programme, it is imperative that both nuclear diversity and cytoplasmic diversity are maintained among hybrid parents. In this context, a continuous search for new CMS‐inducing cytoplasms is necessary. This paper reports detection of maternal inheritance of male sterility in the progeny derived from a natural hybrid between a wild relative [Cajanus lineatus (W. & A.) Maesen comb. nov.] of pigeonpea and an unknown pigeonpea [Cajanus cajan (L.) Millsp.] genotype. In the present study, the male sterility was maintained up to BC7F1 generation by an advanced breeding pigeonpea line ICPL 99044. This male sterility inducing cytoplasm of C. lineatus was tagged as A6. In future, this CMS genetic stock can be used to develop a range of new pigeonpea hybrids with high yield and adaptation.

Genetics of fertility restoration and agronomic performance of CMS based hybrids in pigeonpea

Genetics of fertility restoration and agronomic performance of CMS based hybrids in pigeonpea

Identification of new fertility restorers for development of early maturing pigeonpea hybrids

The paper reports the identification of two early maturing fertility restorers viz.ICPR 2433 and ICPR 2438. The fertility restoration was found to be under the control of two duplicate dominant genes. Multi-location evaluation of the hybrids involving these restorers revealed that the fertility restoration of the hybrids was stable across seven environments. On average, the two hybrids (ICPH 2348 and ICPH 2433) out-yielded the control ICPL 88039 by a margin of over 100%. These results showed that with targeted breeding and selection of fertility restorers it would be possible to breed early maturing hybrids in the near future.

Identification of new fertility restorers for development of early maturing pigeonpea hybrids

The paper reports the identification of two early maturing fertility restorers viz.ICPR 2433 and ICPR 2438. The fertility restoration was found to be under the control of two duplicate dominant genes. Multi-location evaluation of the hybrids involving these restorers revealed that the fertility restoration of the hybrids was stable across seven environments. On average, the two hybrids (ICPH 2348 and ICPH 2433) out-yielded the control ICPL 88039 by a margin of over 100%. These results showed that with targeted breeding and selection of fertility restorers it would be possible to breed early maturing hybrids in the near future.

Pigeonpea breeding in eastern and southern Africa: challenges and opportunities

AbstractPigeonpea (Cajanus cajan[L.]Millspaugh) is an important multipurpose grain legume crop primarily grown in tropical and subtropical areas ofAsia,Africa andLatinAmerica. InAfrica, the crop is grown for several purposes including food security, income generation, livestock feed and in agroforestry. Production inEastern andSouthernAfrica (ESA) is however faced with many challenges including limited use of high‐yielding cultivars, diseases and pests, drought, under‐investment in research and lack of scientific expertise. The aim of this review is to highlight the challenges facing pigeonpea breeding research inESAand the existing opportunities for improving the overall pigeonpea subsector in the region. We discuss the potential of the recently available pigeonpea genomic resources for accelerated molecular breeding, the prospects for conventional breeding and commercial hybrid pigeonpea, and the relevant seed policies, among others, which are viewed as opportunities to enhance pigeonpea productivity.

Studies on Gene Action and Combining Ability of Cytoplasmic-Genic Male Sterility System based Hybrids in Pigeonpea [<i>Cajanus Cajan</i> (L.) Millsp.

The present investigation was undertaken with different newly developed six cytoplasmic male sterile (A) lines and five pollen fertility restorers (R) lines as testers were crossed in a line x tester mating design for ascertaining their general and specific combining ability for yield and its component traits in pigeonpea [ Cajanus Cajan (L.) Millspaugh.]. The mean sum of squares due to line x testers interaction were significant for all the characters except plant height, revealed the significant contribution of hybrids for specific combining ability variance components. The ratio of σ2gca/ σ2sca being more than unity was found for the traits, days to flowering, days to maturity, plant height and biological yield, which indicated greater role of additive genetic variance for the inheritance for these traits suggesting and indicated to further improvement as a source of favourable genes for earliness and yield improvement through selection of desired transgressive segregants from segregating generation. The ratio σ2gca/ σ2sca being less than unity was found for the traits, number of branches per plant, number of pods per plant, number of seeds per pod, pod length, 100-seed weight, seed yield per plant, harvest index, protein content and leaf area, which exhibited greater role of non- additive genetic variance for the inheritance for these traits and indicated to exploitation of these traits for improvement of yield through heterosis breeding. Among parents, CMS GT 603 A (28.43) and GTR 95 (17.24) were good general combiner for seed yield and its contributing traits viz . pod length, number of branches per plant, number of pods per plant, number of seeds per pod, pod length, biological yield and leaf area, CMS GT 33 A (0.48) and CMS GT 301 A (0.19) for protein content, CMS GT 33 A (-17.93), CMS GT 288 A (-9.03), GTR 52 (-1.40) and GTR 8 (-0.62) recorded for earliness. These parents can be improved further through intensive crossing programme and subsequent selection of transgressive segregants in desired direction. Hybrids CMS GT 33 A X GTR 18 (29.31), CMS GT 302 A X GTR 8 (25.27), CMS GT 601 A X GTR 52 (21.35) and CMS GT 288 A X GTR 95 (20.89) were the best for seed yield per plant . These crosses had also high sca values for its contributing traits viz . number of branches per plant, number of pods per plant, pod length, harvest index, biological yield and leaf area. These crosses involved poor x average, poor x poor and average x poor combining parents and better performance reflected involvement of interaction of dominant and epistasis type gene action for this trait. So, these crosses can be exploited through hybrid breeding programme.

Studies on Gene Action and Combining Ability of Cytoplasmic-Genic Male Sterility System based Hybrids in Pigeonpea <i>Cajanus Cajan</i> (L.) Millsp.

Studies on Gene Action and Combining Ability of Cytoplasmic-Genic Male Sterility System based Hybrids in Pigeonpea <i>Cajanus Cajan</i> (L.) Millsp.

Growth, yield attributes and yield of medium duration pigeonpea hybrid ICPH-2671 as influenced by fertility levels and planting geometry

A field experiment was conducted during <italic>Kharif</italic> season 2009 to study the response of hybrid pigeonpea to planting geometry and fertility levels. The results revealed that the hybrid pigeonpea ICPH-2671 recorded significantly higher grain yield (2.40 tha<sup>−1</sup>) as compared to cv. Maruti (1.68 t ha<sup>−1</sup>) and the magnitude of increase was 41.7 % higher. The yield parameters like grain weight plant<sup>−1</sup>, number of pods plant<sup>−1</sup> and growth parameters like number of primary and secondary branches plant<sup>−1</sup>, LAI and dry matter production and its distribution were higher with hybrid pigeonpea ICPH-2671 compared to variety Maruti. Significant differences were observed among the plant geometry and fertility levels and their interactions with respect to growth and yield parameters. The plant geometry of 90 cm x 45 cm recorded significantly higher grain yield (2.57 t ha<sup>−1</sup>) as compared to closer geometry of 60 cm x 30 cm (2.19 t ha<sup>−1</sup>). The fertility level of 50: 100 N, P kg ha<sup>−1</sup> resulted in significantly higher grain yield (2.57 t ha<sup>−1</sup>) as compared to lower fertility level of 25:50 N, P Kg ha<sup>−1</sup> (2.23 t ha<sup>−1</sup>).

Genomics for greater efficiency in pigeonpea hybrid breeding.

Cytoplasmic genic male sterility (CGMS) based hybrid technology has demonstrated its immense potential in increasing the productivity of various crops, including pigeonpea. This technology has shown promise for breaking the long-standing yield stagnation in pigeonpea. There are difficulties in commercial hybrid seed production due to non-availability of field-oriented technologies such as time-bound assessment of genetic purity of hybrid seeds. Besides this, there are other routine breeding activities which are labor oriented and need more resources. These include breeding and maintenance of new fertility restorers and maintainer lines, diversification of cytoplasm, and incorporation of biotic and abiotic stress resistances. The recent progress in genomics research could accelerate the existing traditional efforts to strengthen the hybrid breeding technology. Marker based seed purity assessment, identification of heterotic groups; selection of new fertility restorers are few areas which have already been initiated. In this paper efforts have been made to identify critical areas and opportunities where genomics can play a leading role and assist breeders in accelerating various activities related to breeding and commercialization of pigeonpea hybrids.

Identification of fertility restorers, stable combiners and heterotic combinations across environments in pigeonpea [<em>Cajanus cajanifolius</em> (L.) Millsp.] in India

Efficient and stable cytoplasmic genic male sterility system is a prerequisite for commercial exploitation of heterosis in any crop improvement program. The present investigation was undertaken to identify fertility restorers, stable combiners and best heterotic crosses in pigeonpea [Cajanus cajanifolius (L.) Millsp]. Totally, 75 crosses were developed by using three A4 cytoplasm-based male sterile lines viz., ICPA 2047, ICPA 2092 and ICPA 2089, and 25 diverse inbred lines. The pollen fertility assay identified 15 good restorers with 85-95% fertility status. The 45, best restored combinations identified were assessed across four seasons (August and September, 2012 and 2013) for their stable heterosis and general and specific combining ability to identify parents possessing desirable genes. Variance for combining ability was significant (p<.05) for lines, testers and line × tester effects. Among the three male sterile lines, ICPA 2047 was stable with a significant general combining ability for most of the traits followed by ICPA 2092, while the general combining ability effects among males was high across seasons for ICPL 20205 and ICPL 20177 (p<0.05). The cross combination of ICPA 2089 × ICPL 20205 had desirable genes for days to the first flowering, 50% flowering and maturity. For yield related traits, cross combinations of ICPA 2047 × ICPL 20128, ICPA 2092 × ICPL 11376 and ICPA 2047 × ICPL 20107 had significant specific combining ability indicating their usability in development of hybrids (p<0.05). With respect to the heterotic ability of crosses, crosses involving parents ICPA 2089 as female and ICPL 88034 and ICPL 81-3 as males showed negative heterosis for flowering and maturity. For yield related traits, crosses with ICPA 2047 as the female parent and ICPL 20128, ICPL 20177 and ICPL 20096 as the male parents showed significant positive heterosis (p<0.05). The identified parents with good combining ability and cross combination`s with significant heterosis could be utilized in producing high yielding hybrids in pigeonpea.

Dry matter production, it's partitioning, yield and nitrogen addition to the soil through leaf litter of hybrid pigeonpea

In the present investigation, transplanted hybrid pigeonpea recorded significantly higher seed yield as compared to dibbled hybrid pigeonpea. Significantly higher yield obtained under transplanted method was due to positive association between yield attributing characters. At harvest, total dry matter production plant -1 was significantly higher with transplanted method as compared to dibbled hybrid pigeonpea. Higher total dry matter production plant -1 with transplanting was due to higher dry matter accumulation in stem, leaves and reproductive parts over dibbling at different growth stages. Planting geometry of 120 cm × 90 cm produced significantly higher seed yield over 90 cm × 30 cm and 90 cm × 60 cm.

Genomics-assisted breeding for boosting crop improvement in pigeonpea (Cajanus cajan).

Pigeonpea is an important pulse crop grown predominantly in the tropical and sub-tropical regions of the world. Although pigeonpea growing area has considerably increased, yield has remained stagnant for the last six decades mainly due to the exposure of the crop to various biotic and abiotic constraints. In addition, low level of genetic variability and limited genomic resources have been serious impediments to pigeonpea crop improvement through modern breeding approaches. In recent years, however, due to the availability of next generation sequencing and high-throughput genotyping technologies, the scenario has changed tremendously. The reduced sequencing costs resulting in the decoding of the pigeonpea genome has led to the development of various genomic resources including molecular markers, transcript sequences and comprehensive genetic maps. Mapping of some important traits including resistance to Fusarium wilt and sterility mosaic disease, fertility restoration, determinacy with other agronomically important traits have paved the way for applying genomics-assisted breeding (GAB) through marker assisted selection as well as genomic selection (GS). This would accelerate the development and improvement of both varieties and hybrids in pigeonpea. Particularly for hybrid breeding programme, mitochondrial genomes of cytoplasmic male sterile (CMS) lines, maintainers and hybrids have been sequenced to identify genes responsible for cytoplasmic male sterility. Furthermore, several diagnostic molecular markers have been developed to assess the purity of commercial hybrids. In summary, pigeonpea has become a genomic resources-rich crop and efforts have already been initiated to integrate these resources in pigeonpea breeding.

Yield, yield parameters and economics of hybrid pigeonpea (cv. Icph-2671) as influenced by planting methods and geometry

A field experiment was conducted at Agricultural Research Station, Annigeri (district Dharwad) during Kharif , 2011 to evaluate the performance of the planting methods and geometry of recently released pigeonpea hybrid ICPH-2671. The results revealed that the transplanted hybrid pigeonpea recorded significantly higher seed yield (1899 kg ha ?1 ) and net returns (Rs. 36,005 ha ?1 ) as compared to dibbled hybrid pigeonpea (1376 kg ha ?1 , Rs. 23,531 ha ?1 , respectively).

Effects of cytoplasm fromCajanus cajanifoliuson the performance of pigeonpea hybrids

This research communication reports results of the first study on the influence of cytoplasm on the performance of CMS-based pigeonpea hybrids. In this study two isonuclear lines with diverse cytoplasm were compared in hybrid combinations involving seven inbred fertility restorers. Pusa Ageti-(F) had cultivated pigeonpea cytoplasm, while Pusa Ageti-(A4CMS) carried the cytoplasm of a wild species Cajanus cajanifolius. The trials conducted over two seasons, showed small cytoplasmic effects on the traits studied. For seed yield the hybrids with cultivated cytoplasm were better in performance; however the extent of the superiority of these hybrids varied. The greatest yield penalty of 19.1% due to the cytoplasm of the wild species was recorded in cross involving restorer line R-2364. For other traits no definite trend was observed in favour of any specific cytoplasm. The cytoplasmic effects on the hybrids also appeared to be influenced by genetic variation in the pollinator lines.

Molecular diversity based heterotic groups in pigeonpea [Cajanus cajan(L.) Millsp.

A set of 155 hybrid parents was characterized at molecular level using 24 simple sequence repeat (SSR) markers. The number of alleles amplified ranged from 3 to 41 at an average of 14.5 alleles per marker and mean polymorphic information content (PIC) value of 0.64. Based on genetic diversity, three heterotic groups were constituted. Male sterile (A) lines were distributed into two heterotic groups, while the fertility restorer (R) lines formed three heterotic groups. Of the 135 restorers studied, 51 (37.78%) were classified in heterotic group I, and 75 (55.56%) in heterotic group II. Six interspecific derivatives and three other genotypes constituted the heterotic group III. These observations indicated the presence of limited genetic diversity among A and R lines. Based on the present results, it is recommended that for breeding high yielding pigeonpea hybrids, more attention be given to develop new genetically diverse hybrid parents.

A Study on Comparative Fertility Restoration in A2 and A4 Cytoplasms and Its Implication in Breeding Hybrid Pigeonpea [Cajanus cajan (L.) Millspaugh

Exploitation of hybrid vigour has been visualized as the most efficient option for increasing productivity in pigeonpea [Cajanus cajan (L.) Millspaugh]. Cytoplasms from various wild relatives of pigeonpea have been transferred to develop CMS lines in the background of cultivated pigeonpea. However, A2 (Cajanus scarabaeoides) and A4 (Cajanus cajanifolius) cytoplasms have been utilized most frequently. In order to study fertility restoration efficiency in F1 hybrids having either A2 or A4 cytoplasms, an experiment was conducted at the Indian Institute of Pulses Research (IIPR), Kanpur during 2008-2012. Four CMS lines namely Hy4A, H28A (each with A2 cytoplasm), ICP 2039A and ICP 2043A (both with A4 cytoplasm) were crossed with ten genotypes/restorers of long duration pigeonpea for two years. The F1 hybrids so-obtained were assessed in the succeeding years for pollen fertility and pod setting. All the pollinators except IPA 203 restored fertility in F1 hybrids derived from ICP 2039A and ICP 2043A (both having A4 cytoplasm). However, none of the restorers were effective in restoring fertility in hybrids derived from Hy4A and H28A (each with A2 cytoplasm). This could be ascribed to undesirable linkage drag still present in these two CMS lines having A2 cytoplasm. The F2 progenies derived from 4 hybrids (ICP 2039A × NA-1, ICP 2039A × Bahar, ICP 2043A × NA-1 and ICP 2043A × Bahar) segregated approximately into 3 fertile: 1 sterile plants. However, 2 F2 progenies having Pusa 9 as the restorer revealed approximately 15 fertile:1 sterile ratio. Thus monogenic and digenic duplicate gene action with complete dominance for fertility restoration was observed in F1 hybrids derived from CMS lines having A4 cytoplasm. F3 progenies from individual F2 plants of these crosses also confirmed the same pattern of fertility restoration. This study indicated that CMS lines based on A4 cytoplasm would be more desirable as these might have more number of restorers compared to those having A2 cytoplasm.

From concept to field: evolution of hybrid pigeonpea technology in India

The role of hybrid vigour in the enhancement of productivity is well recognized. Its application, however, has been restricted to a few crops and legume breeders could never take its advantage due to various seed production issues. Recently, plant breeders have succeeded in creating the world's first commercial hybrid in a food legume, popularly known as red gram or pigeonpea [Cajanus cajan (L.) Millsp.]. This was possible due to success in breeding a stable cytoplasmic nuclear male sterility (CMS) system and exploitation of its partial natural out-crossing. This development has provided golden opportunities to break the decades-old yield plateau in this crop. Among the hybrid combinations evaluated, ICPH 2671 and GTH 1 were found most promising. In the on-farm trials ICPH 2671 recorded 46.5% superiority over the best available cultivar Maruti; while GTH 1 was 33.9% superior to the control, and it was released in Gujarat state in 2004; but for some reasons associated with its stability of fertility restoration it failed to reach the level of commercialization. The outstanding performance of hybrid ICPH 2671 led to its release by both, a private seed company as ‘Pushkal’ and by the state Government of Madhya Pradesh as ‘RV ICPH 2671’ in 2010. The journey of the evolution of hybrid pigeonpea technology was fascinating and challenging. It took a long time of over 39-years from its conceptualization to finally reaching Indian farmers. The impact of this breakthrough was visible when two more hybrids ICPH 2740 and ICPH 3762 were recently released in India. Since it is a path breaking research among food legumes, an attempt has been made here to archive the milestones of this historic plant breeding event.

GGE biplot based assessment of yield stability, adaptability and mega-environment characterization for hybrid pigeonpea (<i>Cajanus cajan</i>)

GGE biplot methodology is a powerful tool to study relationship among test environments (E), genotypes (G) and genotype-by-environment interaction (GE). Present study was conducted on 10 short-duration genotypes in five test environments for two years, and 16 medium-duration genotypes in six test locations for three years in randomized complete block design with two replications. In short-maturity group three mega-environments (ME) were found—ME1 comprised of Phaltan, Patancheru and Hyderabad1; ME2 and 3 constituted Jalna and Aurangabad, respectively. In scenario of limited resources, Patancheru may be a good testing location for general adaptability of short-duration hybrids, while Aurangabad and Hyderabad1 may be right environments for testing specific adaptation of short-duration cultivars in pigeonpea. ICPH 2433 was a winning genotype in ME1 in terms of high yield and stability. In medium-maturity group, two MEs were observed. Jalna, Jalna 1, Parbhani and Hyderabad grouped together as ME1, while Patancheru and Phaltan formed the second mega-environment (ME2). Parbhani was found to be most representative of all the six test locations. Jalna (ME1) and Phaltan (ME2) produced longest environment vectors, and hence may be regarded as highly discriminating. In medium- maturity group ICPH 2673 was found to be stable and high-yielding genotype for ME1.

English

Hybrid pigeonpea [Cajanus cajan (L.) Millsp.] breeding technology based on cytoplasmic male sterile (CMS) was recently developed in India. A program was initiated to track the purity of female parental lines by incorporating an obcordate leaf shape marker in established male sterile A-lines. Seven obcordate A-lines developed by backcrossing and selection were crossed with four known fertility restorers in line x tester mating design to study their general and specific combining ability. Higher magnitude of specific combining ability (SCA) effect showed that, hybrid yield was under the control of non-additive genes. Among A-lines, ICPA 2204 was the best general combiner. Among testers, ICPL 20116 was the best general combiner. Among hybrids, ICPA 2208 x ICPL 20108 a cross between high general combining ability (GCA) parents was the best with positive significant SCA effect and higher mean performance for grain yield, 100-seed mass, number of seeds/pod and resistance to fusarium wilt disease. The success of this technology will help to address the issue of seed purity to some extent. Key words: Combining ability, line × tester, general combining ability (GCA) and specific combining ability (SCA), obcordate leaf shape, pigeonpea.