A field experiment was conducted at Coimbatore (11° N, 77° E), India during the 1996 and 1997 crop seasons, using four commercial sugarcane varieties (Co 8021, Co 419, Co 8208 and Co 6304), to study the effect of three levels of drought (severe, moderate and control) during the formative phase (60–150 days after planting) on growth determinants and their relationship with dry matter accumulation. The reduction in dry matter content was 60.8, 52.4 and 25.9 % in severe drought and 46.3, 36.3 and 15.1 % in moderate drought at the ends of the formative, grand growth and maturity phases, respectively. High net assimilation rate, optimum leaf area index, high crop growth rate and an early shift in dry matter allocation to the stem were found to be desirable for higher biomass production, especially under water‐limited drought conditions. Measurement of growth parameters such as net assimilation rate, relative growth rate, leaf area index and leaf area duration under drought and crop growth rate and stalk elongation rate under normal irrigated conditions, particularly during the formative phase, might help to predict total dry matter at harvest. Leaf area ratio was not found to correlate with total dry matter at harvest in either drought or normal irrigated conditions.
Field experiments were conducted at Coimbatore, India to study the effect of three levels of drought (severe, moderate and no drought) during the formative phase (60–150 days after planting; DAP) of sugarcane on the tillering, the conversion of shoots to millable canes, cane attributes and the quality of different classes of shoots in four sugarcane cultivars (Co 8021, Co 419, Co 8208 and Co 6304)_the different classes of shoots studied were: mother shoots (which emerged 0–30 DAP), early tillers (30–60 DAP), mid‐season tillers (60–150 DAP) and late tillers (150 DAP). The results indicated that drought during the formative phase reduced the total number of shoots and their conversion to millable canes at harvest. Drought also reduced the cane length, number of inter‐nodes and single cane weight of different classes of shootsand the subsequent total cane yield. Irrespective of drought treatments, Co 8021, a high‐tillering, thick‐stalked cultivar, gave the highest cane yield despiteits higher shoot mortality, while Co 8208, a low‐tillering, thin‐stalked cultivar, gave the lowest cane yield despite its lower shoot mortality. Thus a moderate level of shoot mortality is clearly necessary to obtain higher millable canes and subsequently higher cane yield. Mother shoots and early tillers together contributed most of the total number of millable canes (84.5 %) and of the total cane yield at harvest (86.2 %). The contribution of late tillers to the number of millable canes and cane yield was, however, negligible, especially in cultivars Co 6304 and Co 8208. There was a gradual reduction in stalk attributes such as cane length, number of internodes, single cane weight and commercial cane sugar percentage as the physiological age of shoots decreased. This study emphasizes the need for a cultivar with the optimal characteristics of early tillering (like Co 8021 and Co 6304) and maximum conversion to millable canes (like Co 8208) and provides information relevant to breeders making decisions on crossing programmes to produce improved cultivars for drought conditions.
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