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Drought is one of the important problems that drastically affect sugarcane production in several countries. The objective of this research was to investigate the effects of early drought stress on physiological parameters and agronomic traits of six sugarcane genotypes under field conditions. The experiment was arranged in a split plot in a completely randomized block design with three replications. The main plot was represented by three different water regimes: field capacity (FC), ½FC and rain-fed (RF), whereas the subplot consisted of six sugarcane genotypes: KK3 (drought tolerant), Q117 (drought tolerant), LK92-11 (drought susceptible), Ths98-271 (S. spontaneum), KK08-214 (the F1 hybrid derived from S. spontaneum × S. officinarum) and E08-4-019 (the F1 hybrid derived from Erianthus sp. × S. officinarum). The six sugarcane genotypes were subjected to three irrigation treatments. The 45-day-old plants of all sugarcane genotypes were exposed to drought by withholding water for 72 days. Certain photosynthetic parameters were measured in the leaves of four-month-old plants. Certain cane yield parameters were measured in the 12-month-old plants. The results showed that early drought stress decreased the maximum quantum yield of PSII efficiency, net photosynthetic rate, transpiration rate and stomatal conductance. Drought stress significantly (p ≤ 0.01) decreased cane yield. The cane yield and sugar yield of KK3 were significantly (p ≤ 0.01) higher than those of the other genotypes. The wild-type sugarcane and the F1 hybrids derived from the wild and commercial sugarcane could maintain better photosynthetic performance while encountering early drought stress.

We examined quantitative traits in leaf anatomical characteristics in 20 chromosomal segment substitution lines (CSSLs) of rice cultivar Khao Dawk Mali 105 (KDML105) carrying drought-tolerant quantitative trait loci (DT-QTL) segments from drought-tolerant donors. Two DT-QTL donor lines DH103 and DH212, drought-sensitive recurrent parent KDML105, and two drought-tolerant standard checks CT9993 and IR62266 (parental lines of DH103 and DH212) were also included for comparison. A total of 20 quantitative leaf anatomical characters were evaluated from fully expanded leaves of greenhouse-grown 30-day-old plants. The results showed that the studied rice lines displayed variations in their leaf dimensions, with the four drought-tolerant lines and almost all 20 CSSLs exhibiting wider leaves, higher number of small and total vascular bundles, higher stomatal density, and shorter stomatal length than those of KDML105. Eleven out of 20 characters were selected for principal component analysis and the studied lines were categorized into 7 groups, with the drought-tolerant standard check CT9993 clearly isolated from the others due to its outstanding characters. CSSL-9, which shared major similarities of quantitative traits to CT9993, fell outside its CSSL group. The characters related to drought tolerance ability were shared between the improved CSSL lines and the drought-tolerant lines, but differed from KDML105 and included the wider leaves, the higher number of small and total vascular bundles, and denser but smaller stomata.

Sucrose loss after harvest is one of the serious problems for sugar factories especially when the time lag between harvesting to milling of sugarcane is extended during a period of high ambient temperature. This study was undertaken to test the hypothesis that storage temperature and duration affect acid invertase activities and sugar levels in harvested sugarcane stalks. Weight loss, the activities of soluble acid invertase (SAI) and cell wall acid invertase (CWI), and sugar levels were determined in two commercial sugarcane cultivars, K84-200 and K88-92 during storage at 25 o C and ambient temperature (23 -32 o C). The harvested stalks stored at ambient temperature lost more fresh weight and sucrose than those kept at 25 o C. They also had higher reducing sugar content and SAI activity. At ambient temperature, the SAI activity had strong relationship with storage duration, sucrose and reducing sugar levels. These results indicate that storage temperature and duration had significant influence on metabolic changes of sugars and related enzyme activities in harvested sugarcane stalks.

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