Feasibility of heterosis breeding in pigeonpea

Scientific expertise and knowledge developed in the world is now easily accessible. But how quickly, efficiently and effectively one can handle the problem will depend on the strategy planned. Development of a particular approach in crop improvement is based on the convenience. The convenience is decided by various considerations such as the status of the crop improvement work, available varieties and germplasm in relation to the target. These points make one to enter into either technically easy or complicated strategies. Other considerations are about the resources in terms of manpower, finance, field and laboratory facilities available at the disposal of a plant breeder.

Pigeonpea improvement in early ages started with limited resources. Selection from landraces were tried by the breeders. Later it was emphasized to incorporate resistance to major diseases like Fusarium wilt and sterility mosaic. Unfortunately the pigeonpea improvement was restricted to conventional breeding until last few decades, may be due to limitations on resources available and could not achieve gains in productivity potential (Saxena, 2002) to cope up with increasing demand. In recent years increasing demand for pulses on one hand and limited availability on the other, invited attention of many countries as the crop for export to Indian subcontinent. It has now greater value than any time in past and invites research policies to have new non-conventional approaches like heterosis breeding.

Pigeonpea has been considered technically suitable for heterosis breeding due to predominance of non-additive genetic variance for the traits like grain yield and other important yield components (Reddy et al. 1981, Sidhu and Sandhu, 1981; Saxena and Sharma, 1990). Germplasm presents wide rage of genetic diversity. Abundant natural out pollination (Saxena et al. 1990) can be utilized to avoid tedius hand pollination. The need of male sterility to avoid mechanical emasculation has been fulfilled through discovery of genetic male sterility  (GMS)(Reddy et al. 1978 and Wallis et al. 1981, Wanjari et al. 1995) and CGMS (Tikka et al. 1998; Wanjari et al., 1999 and Saxena et al.,2003). These points favour commercial seed production of F₁ hybrids in pigeonpea, on the basis of which F₁ hybrid breeding using GMS has been attempted successfully to develop six hybrids for cultivation in India (IIPR, 2002, Saxena, 2002). However they faced the problems in commercial seed production. The pigeonpea breeders in India are now trying hybrid pigeonpea breeding on the CGMS systems based on the sterile cytoplasm from Cajanus scaraboides and C. cajanifolius.

Prospective in hybrid technology:

Saxena (2002) opined that the experiences with genetic male sterility based hybrid technology in the past 25 years has conclusively demonstrated that the exploitation of hybrid vigour is feasible if the seed production difficulties are addressed adequately. The male sterility has been now diversified in indeterminate good agronomic bases in early as well as mid-late or late group of pigeonpea and more than two dozens of male sterile lines with better potential of seed yield are available. These can be successfully utilized to have more productive hybrids.

In Central and South India, large proportion of the area is under medium duration pigeonpea under various intercropping system, where lower seed rate of 1 to 3 kg ha^-1 is used. This is one of the favourable points for the promotion of hybrid pigeonpea. AKPH-2022 has been the first medium duration hybrid released from Dr.Panjabrao Deshmukh Krishi Vidyapeeth, Akola which may have a better prospects under such situations more particularly in Maharashtra, Andhra Pradesh and Karnataka.

A package of GMS based technology for hybrid pigeonpea seed production has been developed through various considerations to improve the seed yield (Vishwa Dhar et al. 2002). It has been successfully demonstrated on the farmers field and has found to be acceptable to the seed growers. Further efforts to identify large number of morphological seedling marker traits (Patil et al. 1998) and to establish linkage of few of them with the genetic male sterility are in progress (Wanjari, 2002). It will facilitate rouging fertile segregants in early seedling stage.

Development of stable cytoplalsmic male sterility (Tikka et al. 1998; Wanjari et al., 1999 and Saxena et al.,2003) and further efforts to establish restorers (Tikka et al. 1998; Patel, 2001; Saxena, 2002) opened new avenue to work on hybrid pigeonpea. Chavan et al. (2004) established good number of fertility restorers for the CMS based on C.scrabaeoides. Wanjari and Patel (2003) reported few restorers able to produce hybrids which can set autogamms pod setting. Rigorous efforts will, however, be needed to purify the parental lines and to develop the hybrids based of A-B-R system of cytoplasmic genetic male sterility. 

Let us hope for better hybrids in near future.