Studies on male sterility in onion (Allium cepa L.)

Abstract

The main objectives of the investigation were to study, “Development and morphological analysis of flowers, Micro-sporogenesis and Micro-gametogenesis; seed set and seed yielding abilities of male fertile and male sterile lines. The salient achievements are summarized below. Developmental and morphological analysis of male sterile and male fertile plants: The flower buds of male sterile and male fertile lines took 97.3 and 105.5 days respectively from the time of visible initiation to complete withering of filaments. The male sterile line had flower bud size 0.6 x 0.6 Sq.cm. This was comparatively less than that of male fertile line 0.8 x 0.9 Sq.cm. The total flowering period observed in both sterile and fertile lines was 22.3 and 24 days respectively. Peak flowering was observed on 15th day in sterile whereas on 17th day in fertile line from the visible flower initiation. Majority of the flower buds (22-34%) opened between 7 a.m. and 10 a.m. in male sterile line. Whereas in fertile line between 7a.m. and 4a.m. Peak period of anthesis was observed at 7 a.m. in both male sterile (34%) and male fertile (16%) lines. Maximum anther dehiscence was at 11 a.m. (100%). The lines MS11,MS48 and Arka Kalyan were more receptive on 3rd day of crossing with 96,93 and 91% seed set respectively whereas, MS39 and MS65 were receptive till 5th day of crossing after opening, with 100% and 97% seed set respectively. Arka Kalyan recorded the highest pollen germination (50-75%) with the lowest pollen absorption (21.76%).Studies on micro-sporogenesis and microgametogenesis in onion flower: Studies showed that the tapetum in male fertile lines was essentially peripheral type. Following the release of microspores from tetrads, radial and inner tangential walls of the tapetum broke down and the tapetal protoplast released into the locular cavity and engorged the developing microspores. Whereas the sterile lines used in the present investigation exhibited abnormalities. Soon after the formation of microspores. Investigation on seed set and seed yielding abilities of male sterile and male fertile lines revealed that the Pusa Red (42), Arka Pragathi (42.97), MS 48(38.57) and MS39 (40.37) recorded lower number of days for flower stalk emergence. Arka Pithamber (84.43) and MS48 (98.5) were found to had highest percent flowering. Arka Niketan recorded highest seed weight per plant (3.28g). Arka Pithamber had highest umbel weight (12.03g). The parental lines did not show significant differences for number of flowers per umbel, number of seeds per umbel percent recovery of seeds per umbel and seed set percentage. The crosses which had significant differences for different characters were plant height MS11 x Arka Bindu (68.28 cm); number of days for stalk emergence MS48 x Arka Bindu (98.50); highest percent flowering MS11 x PBR-2(96); number of flower stalks MS39 x Arka Kalyan (6); highest length and diameter of the scape MS39 x PBR-1(707.27 x 1.47 Sq.cm); highest umbel size index MS65 x Arka Kalyan (25.19); number of seeds per flower MS48 x PBR-2(42); highest seed weight per umbel MS39 x Arka Bindu (1.33 g); seed weight per plant MS11 x Arka Pithamber (7.27 g); umbel weight MS11 x PBR-1 (6.23 g); 1000 seed weight MS65 x Arka Niketan. Correlation studies for different characters among parental lines and crosses Study revealed that the strong positive correlation for umbel diameter and umbel weight (r=0.967), seed weight per umbel were recorded between seed weight per plant (r=0.788) and umbel size index (r=0.657). Umbel weight recorded positive correlation between seed weight per umbel(r=0.776), seed weight per plant (r=0.632) and umbel size index (r=0.816). Strong correlation among the crosses were observed between percent flowering and plant height (r=0.51) and umbel diameter (r=0.515). Between number of days for stalk emergence and umbel index (r=0.512), seed weight per umbel (r=0.381), umbel equatorial diameter (r=0.722) and umbel weight. Seed weight per umbel had significant correlation for seed weight per plant (r=0.592) and umbel weight (r=0.444) in turn seed weight per plant recorded positive correlation for number of flower stalks per plant (r=0.529).