Heterosis for seed yield and its relationship with genetic divergence in grasspea (Lathyrus sativus L.)

Heterosis has been a phenomenon of great interest for Plant Breeders and its utilization has led to the considerable yield improvement in crop plants. Keeping in view, the present investigation was conducted to study the nature and extent of genetic diversity available in this crop under northwestern Himalayas. Twenty-four landraces were collected from different agroclimatic locations and raised in Randomized Complete Block Design with three replications in the experimental farm of Himachal Pradesh Krishi Vishvavidyalaya, Palamppur, during rabi 1994-95. To study the relationship between heterosis over the better parent and genetic divergence, five genetically diversed parents (LSP-1, LSP-2, LSP-3, LSP-4 and LSP-5) were crossed in a half-diallel fashion. All the fifteen populations were raised in randomized complete block design with three replication during rabi 1995-96. The observation on plants height, number of branches, days to flower, days to podding, days to maturity, pods/plant, seeds/pod, 100-seed weight, seed yield/plot and seed neurotoxin content were recorded at appropriate stages. The seeds were analyzed biochemically as per the standard procedure. The analysis of variance revealed the presence of considerable genetics variability for all characters except for days to maturity. Using Tocher's procedure,twenty four lines could be grouped into five clusters, three of which contained only a single line each. Clusters I contained the maximum number of 19 lines. LSP-19 (white flower) and LSP-20 (pink flower ) clustered with blue flowered lines. Likewise, LSP-20 (lowest ODAP) clustered with other high ODAP lines including LSP-11 (highest ODAP) which suggested that the flower color and ODAP content were not the cause for genetic diversification in Lathyrus sativus L. The study revealed an appreciable heterotic response over better parents in desired direction for a number of characters. A highest positive and significant heterosis for seed yield (28.7%) was exhibited by the cross LSP-2 x LSP-5 followed by the crosses LSP-3 x LSP-5 (23.0%) and LSP-2 x LSP-3 (16.7%). The cross LSP-2 x LSP-5 also recorded highest heterosis (53.6%) for pods/plants. An examination of the clustering behaviour of fifteen population revealed that seven clusters can be formed, two of which contained only single member each. The cross LSP-2 x LSP-5 though, showed highest heterosis for seed yield yet, its parent did not record maximum divergence. On the other hand, the cross LSP-2 x LSP-3 showed maximum divergence (148.0) between its parental clusters, but, indicated considerable heterotic response for seed yield. This suggested that divergence between parents and percent heterosis did not have one-to-one correspondence for seed yield.