Utilization of Biotechnological and Agronomic Options for Unlocking the Yield Potential of Sweetpotato (Ipomoea batatas (L) Lam.)

Abstract

Sweetpotato (Ipomoea batatas (L) Lam.) is one of the world's highest yielding crops hold promise to combat nutrition and food deficiency especially in the developing countries. This work aims to apply biotechnological tools and agronomic practices such as meristem culture to produce pathogen eleminated plant meterials, callus induction for inducing somaclonal variation, nitrogen, and nitrogen in combination with potassium application for incrising tuber yield. Four cultivars viz. BARI-1 (Tripti), BARI-2 (Kamalasundari), BARI-3 (Daulatpuri) and BARI sweeet potato -4 were used for these experiments. Shoot tips of 3-4 weeks old field grown vines were used for meristem isolation. Explants were surface sterilized with 0.1% mercuric chloride for 6 minutes. MS liquid medium supplemented with 2.0 mg/l Kinetin+0.5 mg/l GA3 and 4% sucrose was found most effective for the primary establishment of isolated apical meristem. For shoot and root development from primarily established apical meristem application of 2.5 mg/l Kinetin+0.5 mg/l GA3 in MS medium was found to be the best. For virus testing, grafting method offeres very low cost options compared to molecular methods. It does not require any special equipment or chemicals. Therefore, plantlets derived from meristem-tips were assayed with virus sensitive indicator plants Ipomoea sestosa using grafting method. The assay revealed most of the mericlones are virus-frees. Virus-tested mericlones were further micropropagated and transferred to nursery for further multiplication. Growing mericlones showed some disease symptoms in the second generation indicating re-infection possibly by viral vectore. Use of 3.0 mg/l Kinetin+0.5 mg/l GA3 and 30% sucrose in MS medium was the most effective for micropropagation of meristem-derived plantlets. Among the studied three explants (internode, root and leaf disc), both internode and root were found good for producing high amount of embryogenic callus. Among the studied different treatments combination of growth regulators, three treatments viz. 2 mg/l 2,4-D+0.5 mg/l NAA, 4 mg/l BAP+0.5 mg/l NAA and 2.0 mg/l TDZ were found very effective in producing embryogenic callus. For plant regeneration from callus 0.5 mg/l BAP+2.0 mg/l 2,4-D was most effective for both internode and root derived callus but for leaves it was 2.0 mg/l zeatin, showing explants-media interaction. The successful acclimatization of the in vitro raised plantlets provides the reproducibility of the developed protocol of using biotechnological techniques. Several somaclones were planted in the field to check their morphological and tuber yield variation. Upon planting in the field condition, several callus-derived plants showed significant variation in their morphological traits. Among these, some somaclones showed better performance in terms of vine length, leaf area and fresh weight of tuberous root. Nevertheless, some were very similar to the mother plants while others are inferior. Among these, some somaclones of BARI-1 showed better performance in terms of vine length, leaf area and fresh weight of tuberous root. On the other hand somaclones of BARI-3 showed poor performance for the same traits. Effect of nitrogen fertilizer has also been studied as one of the main agronomic practices which might affect sweetpotato yield. To test the effect of potassium and nitrogen fertilizer, both conventional vine and disease-free mericlone were tested in this experiment. It was observed that nitrogen fertilizer as urea significantly influences in all vegetative growth traits in both mericlone originated and traditional planting materials. A further increase was observed when both potassium and nitrogen are used combinedly. Tuberous root yields of both the mericlone-derived and traditional planting material were significantly higher than no zero fertilizer treatment groups and peaked at 160 kg/ha urea and 180 kg/ha potash. Fertilizer application positively influenced tuber length and tuber diameter. However, there was no difference in the number of tubers. It was observed that mericlone gave higher tuber yield compared to conventional planting materials in identical fertilizer level. It was revealed that, use of mericlone and the optimal fertilizer can increase up to 70% tuberous yield. From the above study, the results revealed that among all fertilizer doses of NK, 160N+180K treatment gave the highest gross margin and benefit cost ratio (BCR) in both situation Mericlone and conventional. On the other hand, Mericlone plant source of BARI -1 is the best for high yield production of sweet potato. So, treatment Nitrogen and potassium (NK), 160N kg/ha +180K kg/ha and Mericlone plant source of BARI -1 are economically viable for our farmers.