ABSTRACT: Details on growth and yield for cassava planted on different dates are useful for determining suitable genotypes for particular growing seasons. Our aim was to study growth and yield of cassava planted on different dates. Four cassava genotypes (Kasetsart 50, Rayong 9, Rayong 11 and CMR38-125-77) were evaluated using a randomized complete block design (RCBD) with four replications in six growing periods (20 Apr, 25 May, 30 June, 5 Oct, 10 Nov and 15 Dec 2015-2016) at Khon Kaen, Thailand. Soil properties were determined prior to planting, and crop traits and weather data were recorded. The six planting dates had a statistically significant effect on all crop traits. Low temperatures and solar radiation related to low biomass accumulation rates and short periods of linear phases for total crop and storage root dry weights with the 30 June planting date. CMR38-125-77 is likely to be a good genotype with respect to total crop and storage root dry weights at final harvest for almost all growing dates, except for the 20 Apr. Leaf area index (LAI) at 120, 240 and 300 days after planting (DAP), specific leaf area (SLA) at 120 DAP, storage root growth rate (SRGR) during 300-360 DAP and leaf growth rate (LGR) during 60-120 and 300-360 DAP were the components for the physiological determinants of total crop and storage root dry weight. The relationship between these physiological traits and storage root could be useful for cassava breeding.

ABSTRACT Drought is a major cause of potential plant stress in areas of rain fed lowland rice (Oryza sativa L.) cultivation. The characteristics of the root system are important for rice plant adaptation and acquiring water under drought conditions. This study aims to evaluate the root responses contributing the plant adaptation to drought stress of 'KDML105' chromosome segment substitution lines (CSSLs). The rice genotypes were grown in PVC tubes. At 30 d after planting (DAP), the plants were subjected to two water regimes, well-watered and early drought stress. The two experiments were different in water status shown as relative water content and soil moisture content and classified as two stress condition in particular years i.e. mild and severe stress in 2013 and 2014 respectively. Shoot dry weight (SDW) and leaf area (LA) increased by mild stress while root dry weight (RDW) and total root length were increased by severe stress. The comparison between WW and DS in the percentage of SDW, RDW and LA showed that the CSSL#6 was the great maintenance genotype in both 2013 and 2014 as well as the donor parent (DH212) while 'KDML105' showed a decreasing RDW in DS than WW. Root length density of all CSSLs was higher than 'KDML105' in the shallow soil layer (37%), but CSSL#12 was greatest in root length density at the deeper soil layers (76.7%) under mild stress. Interestingly, CSSL#1, #4, #5, #6, #12, #14 and #15 tended to produce a higher root depth (59.6%, 52.0%, 53.6%, 58.6%, 52.7%, 49.7% and 53.3%, respectively) at 30 to 90 cm of soil depth compared to 'KDML105' under severe stress. It is possible that several chromosome segments associated with root depth were introgressed from the donors (DH103 and DH212) through the breeding procedure, which can be used as a promising breeding material in Thailand.

Drought at pod filling reduces growth, yield, and seed quality of peanut (Arachis hypogaea L.) Great root system can reduce yield loss under water stress. There is a lack of information on root traits for peanut genotypes and the relationship between rooting traits and peanut yield under terminal drought. The pot experiments were conducted at Khon Kaen University, Thailand, in 2004-2005 and 2005-2006. A randomized complete block design was used with two factorials set-up with four replicates. Factor A consisted of two water regimes (field capacity and 1/3 available water at 80 d after planting to harvest), and factor B comprised of 11 peanut genotypes. Data were recorded for root traits (root dry weight, root length, root surface, root diameter, and root volume), and peanut yield (pod dry weight, biomass, and harvest index) were measured at final harvest. Terminal drought significantly decrease root characteristics (0.83-1.03 g plant-1 of root dry weight) and peanut yield (7.98-8.89 g plant-1 of pod dry weight). Yield responses to terminal drought were not correlated with root traits except root length and root volume (r = 0.71** and 0.83**, respectively). Some genotype, root traits seem to be correlated with peanut yield under terminal drought. ’KK60-3’ showed high root traits, maintained pod dry weight under terminal drought, whereas Tifton 8 maintained biomass production. ICGV98348 had high root traits, maintained pod dry weight and harvest index under drought conditions. The results suggested that peanut contained high root characters which maintained yield under terminal drought.