Development of Short Statured Varieties of Basmati Rice

Abstract

Basmati rice occupies a vital position in the economy of Pakistan. The country is earning approximately 300 million US $ annually from the export of Basmati but the yield of Basmati rice is very low. Among Basmati varieties Basmati 385 is the predominantly grown variety. Despite its high yielding ability, there is risk of genetic vulnerability to diseases and insect pests due to exotic sources involved in its breeding which is closely associated with the fungus diseases. It therefore seemed imperative to search for alternate dwarfing gene source in the basmati background, for which, a large number of semidwarf mutants were isolated from the radiated segregating populations of rice cultivar Basmati 370. Finally, twelve dwarf mutants (DM) were selected and grown in the field. At maturity observations on morphological traits and physical characters of grain were studied and a wide variation in the morphological characters was observed. A positive and significant correlation of plant height with yield and yield components was observed expect tillers/plants whereas no correlation of plant height with the physical character of grain was found. The reduction in plant height of the mutants is mainly due to reduction in specific internodes. It was also observed that reduction in plant height up to 24% did not adversely affect the yield and yield components. Pleiotropic effect of dwarfism was found on agronomic traits but not on grain quality traits. On the basis of variation in plant height, five selected dwarf mutants along with the parent variety were crossed in a diallel fashion excluding reciprocals for genetic studies. Graphic analysis of six parent diallel crosses for plant height showed non allelic interaction. The removal of interacting parent led to a non-interacting 5 x 5 diallel set. The degree of dominance for plant height in both the cases showed over dominance. The genes with positive effects were more dominant than the recessive which indicated that the section for semi dwarfness will be fairly rapid. The segregating F2 population resulting from the crosses of dwarfs with Basmati 370 showed bimodal distribution with tallness being dominant which fitted 3:1 ratio suggesting that dwarfness I these mutants is controlled by a single recessive gene which indicated that dwarfing gene in DM-15-4 is non-allelic to those other dwarfs. The F2 population of the crosses of dwarfs with DM-15-4 gave a ratio of 9 tall to 7 dwarfs. DM-15-4 (mutant carrying non-allelic dwarfing gene) when crossed with the already existing dwarfing gene (DGWG) viz. IR-6 showed tall F1 and the F2 segregating population gave a 7:9 ratio showing duplicate recessive epistasis, non-allelic to DGWG. From these studies it can be concluded that some of the mutants viz. DM-16-5-1 and DM-28 can be released directly as commercial varieties as substitute of Basmatic-370 while the other mutant like DM-15-4 can be utilized in hybridization programme as an alternate source of dwarfism in order to avoid the risk of genetic vulnerability to various diseases and pests attached to DGWG gene.