Heat stress influences plant growth, development, and productivity. This research was initiated to determine whether differential root sensitivity to heat is important in determining differences in plant heat tolerance. Tepary bean (Phaseolus acutifolius Gray) and heat tolerant (GNUI 59) and heat sensitive (BBL 47) genotypes of common bean (P. vulgaris L.) were used to study leaf gas exchange and growth after exposure to high air temperature combined with either high or low root temperature. The effect of temperature on endogenous abscisic acid (ABA) levels in leaves and roots was determined using an enzyme‐immunoassay technique. High shoot/root temperature (45/45°C) for 5 h reduced carbon exchange rate (CER) and subsequent growth in all genotypes. Maintaining root temperature at 25°C restored CER to nearly the control level. High root temperature decreased endogenous ABA levels in the roots in all genotypes, but increased ABA in the leaves in the tepary bean and BBL 47 without stomatal closure. Water stress or exogenous ABA pretreatment prior to high temperature treatment induced stomatal closure at high air temperature. There were no differences in leaf temperatures between the two root temperatures, suggesting that the lower levels of CER, mesophyll conductance, and growth under high root temperature were due to root rather than to leaf temperature.

This study was conducted to determine the effect of tillage systems and soil organic amendments on rice growth, yield and carbon sequestration on paddy soil. The experiment was conducted by using 2x4 factorials in complete randomized design. The first factor was tillage systems (conventional tillage; to and minimum tillage; t1) and the second factor was soil organic amendments (mungbean; p0, sesbania; p1, sunhemp; p2 and rice straw; p3). The results demonstrated that adding organic matter derived from mungbean to the soil was the highest and significantly different of plant height and carbon stock in rice (P≤0.01). The tillage system and organic matter amendment was not significantly different of rice yield. However, tillage systems with a mungbean amendment tent to increased the rice yield. Soil organic matter was the highest in sumhep amendment in soil as following by sesbania, mungbean and rice straw, respectively. In addition, minimum tillage system can increase carbon sequestration in soil at 15 cm soil depth (P≤0.01).

Drought is a major impediment to a rainfed lowland rice system. Drought tolerance has been associated with proline accumulation in roots and leaves. However, genetic linkage was uncertain. To determine if there is a genetic correlation between proline accumulation and drought tolerance; a total of 220 double haploid lines, their parents (CT9993 and IR62266), and three standard checks (IR20, NSG19 and KDML105) were used in experiments to determine the extent of genetic variation in root characters, proline accumulation, relative water content, visual leaf rolling and drought injury under different intensities of water deficit. Genotypes with high proline content in leaf tissues were more dehydration tolerant, a relatively high water content was maintained, and leaf rolling and senescence were delayed under severe water deficit. However, the ability of rice roots to penetrate deep into the soil was negatively correlated with proline accumulation in leaf tissue. Rice roots are mostly distributed at 0-30 cm soil depth under lowland conditions. Therefore, the ultimate goal to combine high dehydration tolerance with strong root penetration may not be realized in the existing germplasm.