Abstract
Comparative growth analysis was carried out on three edible Dioscorea species in field experiments laid out at
Central Tuber Crops Research Institute, Thiruvananthapuram, India, during 1996 and 1997, mainly to elucidate the growth characteristics of recently developed trailing (T) and dwarf (D) varieties of Dioscorea rotundata in comparison with native species of Dioscorea (D. escuelenta and D. alata) under Asian conditions. The leaf area index (LAI) was the highest for D. alata and least for D. escuelenta. The LAI attained maximum values at fifth month in D. escuelenta and D. alata and at sixth month in D. rotundata (T) and D. rotundata (D). The crop growth rate (CGR) of D. rotundata (T) and D. alata were almost similar but significantly greater than that of D. escuelenta and D. rotundata (D). In D. escuelenta, except for a slight decline at Phase 2 [4-5 months after planting (MAP)], the CGR followed a steady increase and attained maximum value at the last phase (6-7 MAP). The CGR peaked at Phase 2 (4-5 MAP) in D. rotundata (T) and at Phase 3 (5-6 MAP) in D. alata and D. rotundata. The early season advantage of CGR in these species might explain their high-yielding nature. In all the species, except D. rotundata (T), net assimilation rate (NAR) showed an increasing trend with advancing crop age. Dioscorea escuelenta possessed the highest NAR and D. alata had the lowest NAR. Significantly highest relative growth rate (RGR) values that declined towards harvest, were computed during the early phases in all the species. With advancing growth, there was significant decrement in LAR, specific leaf area (SLA), and leaf weight ratio (LWR) due to reduction in LAI due to leaf senescence and greater diversion of photoassimilates for tuber development. The LAR, SLA, and LAI of Asiatic species showed significant positive association with rainfall. Highest harvest index (HI) was computed in D. escuelenta closely followed by D. rotundata (D). The HI was significantly lower in D. alata and D. rotundata (T) due to greater canopy size of these species. However, HI of D. rotundata (T) was slightly higher than that of D. alata.
