Optimization of vine killing date for maximum seed-tuber yield and minimum exposure to late-season aphid vectors in potato

Short-duration and early-bulking potato varieties are well-suited for commercial cultivation in the subtropical Indo-Gangetic plains of India. To maximize seed tuber yield, prevent late-season exposure to aphid vectors, and facilitate the timely planting of wheat crops during the <i>rabi</i> season, it is essential to cut the haulms (vines) of seed potatoes at the earliest possible time. A study was conducted to standardize the optimal vine-killing date for two popular potato varieties in the north-western plains of India, <i>Kufri Pukhraj</i> and <i>Kufri Jyoti</i>, by examining variations in seed yield across different vine-killing dates and assessing the incidence of aphid vectors transmitting potato viruses. Tubers were planted on 15 October for two consecutive seasons, and haulms were cut at 70, 80, and 90 days after planting (DAP), with continuous monitoring of aphid populations. Results showed that total tuber yield and tuber numbers increased with delayed vine-killing. Similarly, the yield and number of oversized tubers significantly rose as the vine-killing date was extended. However, seed-size and undersized tuber yields were largely unaffected, while the number of undersized tubers decreased between 70 and 90 DAP. Further, the gain in total tuber yield and yield of over-sized tubers occurred mainly during 70-80 DAP for <i>Kufri Pukhraj</i> in contrast to <i>Kufri Jyoti</i> where maximum increase occurred between 80 and 90 DAP. Therefore, it is concluded that the optimum time of vine killing for maximum seed tuber yield is directly linked to the tuber growth cycle of individual variety. The period of maximum incidence of aphid vectors varied between the two years. Based on the incidence of <i>Myzus persicae</i>, the seed crops in north-western plains of India should not be extended beyond last week of December although real time monitoring of the aphid incidence is recommended.