PhD

ABSTRACT
The present investigation was undertaken to develop superior inbred lines in bitter gourd through advance generation selection of F1 hybrids and biotechnological approaches through pollination of irradiated pollen and embryo rescue. The experiment was conducted at the Department of Vegetable Science, College of Horticulture, Kerala Agricultural University during the year 2016-2018.
Performance evaluation of sixteen hybrids and five varieties (control) of bitter gourd was conducted and five promising hybrids, MC-142, MC-136, MC-139, MC-138 and MC-133, were selected based on the cumulative index. These hybrids were advanced to F2 and F3 generation. Yield contributing characters such as average fruit weight, fruit diameter, fruit girth, flesh thickness and number of harvests were significantly increased in F3 generation compared to its F2 in MC-138 and MC-139. Fruit length, relative early yield and yield per plant showed a significant increase in F3 compared to its F2 in MC-138. Fruit length, number of fruits per plant, yield per plant and number of harvests have significantly reduced in F3 generation of MC-136 compared to its F2 generation. Nonsignificant variance was observed between F2 and F3 generations of all hybrids for majority of the yield contributing characters. Lower range in the subsequent generation is an indication of attainment of uniformity for these characters.
Negative value of response to selection for earliness parameters have indicated an improvement in the characters in F3 generation through selection in F2. Judicious selection in F2 generation led to a positive response to selection for yield contributing characters in most of the hybrids. The difference between genotypes with respect to its response to selection was apparent. Yield per plant, fruit length, fruit weight and relative early yield have shown negative value for response to selection on MC-136 and MC-133. F2 and F3 generations of all hybrids showed positive value of selection differential for all the yield contributing characters.
Positive value of inbreeding depression for nodes to first male and female flower in F3 generation and cumulative inbreeding depression for most of the hybrids indicated that the improvement in earliness parameters are in a desirable direction, producing male and female flowers at earlier nodes. Inbreeding led to a reduction in the number of days taken for fruit maturity from anthesis in all hybrids. Even though inbreeding depression was observed in F2 generation, an increase in per se performance was noticed in F3 generation of hybrids, MC-142, MC-138 and MC-139 for most of the yield contributing characters. But MC-136 and MC-133 could not regain its potential in F3 through advance generation selection for most of the characters. Loss in vigour after inbreeding was observed for yield per plant, relative early yield per plant, number of harvests and fruit length in MC-136 and MC-133. After successive self pollination, MC-136 also had shown a reduction in flesh thickness and the number of fruits per plant.
Desirable economic segregants were chosen based on earliness and yield contributing characters. Per cent of economic segregants for days to first harvest was the maximum in F2 (64.71 %) (48.00-56.00 days) and F3 generations (100%) (46.00-59.00 days) of the hybrid MC-136. Per cent of economic segregants for yield per plant was the highest in MC-136 (58.82%) (3.54-6.50 kg per plant) and MC-138 (53.19%) (3.83-6.57 kg per plant) in F2 and F3 generations, respectively. Selected segregants can be fixed through inbreeding and selection.
An efficient protocol for in vitro haploid embryo culture was standardized in bitter gourd. Pollen from irradiated flowers was used for pollinating female flowers. All irradiation doses from 10 to 100 Gy induced fruit set in the hybrid MC-139. The mean number of seeds and embryos per fruit decreased significantly as the irradiation dose increased. Treatment T10 (100 Gy) failed to produce embryos and all seeds were empty. The results showed that 90 Gy was the best irradiation dose and 15 days after pollination was the best stage of embryo rescue for haploid recovery. The in vitro seed germination in E20A medium was best for embryo culture.Addition of activated charcoal (3g/ L) in E20A medium has enhanced the root initiation.
The highest percentage of successful plants after 20 days of hardening was noticed in control (81.57 %) followed by T1 (79.10 %), T2 (71.18 %), T3 (70.90 %) and T4 (69.04 %). Significant difference was observed for the plant under the treatment T9 with respect to size of guard cell, pollen grain diameter and number of chloroplasts per guard cell compared to the plants under the treatments T0 to T8. The guard cells in haploid plants had 16.23 micron length, 4.66 micron width, 37.34 micron pollen grain diameter, and contained 6.83 chloroplasts whereas guard cells in diploids had 19.50 to 20.20 micron length, 5.38 to 5.73 micron width, 67.41 to 69.62 micron pollen grain diameter and 11.58 to 12.42 chloroplasts. All other treatments except T9 (90 Gy) produced stainable pollen which indicated the normal diploid nature of plants. Plant developed through pollination with irradiated pollen of 90 Gy (T9) produced only sterile pollen. Moreover, seed set was not observed when it was self pollinated which can be attributed to the haploid (n) status of the plant. Others were showing diploid ploidy level (T0 to T8). The present protocol is a successful strategy for generating haploids in bitter gourd.
In conclusion, results show that inbreeding and selection are efficient to improve the earliness and yield characters in bitter gourd. Pollination by gamma irradiated pollen can induce haploid embryo development in bitter gourd and this is the first successful report in bitter gourd on this aspect.