Diurnal and seasonal variations in the photosynthetic performance and chlorophyll fluorescence of cassava 'Rayong 9' under irrigated and rainfed conditions

Abstract

Diurnal photosynthesis responses of cassava cultivar Rayong 9 ('RY9') three months after planting, grown in a field conditions under irrigated and rainfed conditions, were evaluated during the rainy, cool, and hot seasons. Under the mild conditions of the rainy and cool seasons, net photosynthetic rates (PN) increased in parallel with light intensity and attained the maximum at 13.00 or 11.00 h. In the hot season, PN attained the prominent peak at 9.00 h, after which stomatal conductance decreased rapidly coordinated with declining PN and nonphotochemical quenching was enhanced. Photosynthetically active radiation was the major factor influencing PN in the rainy and cool seasons, whereas vapor pressure deficit was the major factor in the hot season. 'RY9' adapted extremely well in this climate because the maximal quantum yield of PSII photochemistry recovered fully in the evening even under the rainfed conditions in the hot season.

Seasonal Variations in Canopy Size and Yield of Rayong 9 Cassava Genotype under Rainfed and Irrigated Conditions

“…In addition, the irrigated crop had higher photosynthesis than did the rainfed crop at nine MAP because of higher relative humidity in the canopy. In contrast, the rainfed crop had lower relative humidity in the canopy, that induced stomatal closure and limited photosynthesis [46].…”

“…El-Sharkawy [40] reported that the temperature below 20 • C decreased photosynthetic rate. Vongcharoen et al [46] found that leaf photosynthesis was reduced in the cool season. According to Alves [2], cassava increases root growth during the period of six to nine MAP, and this growth phase is critical for cassava yield, because cassava moves assimilates from leaves to storage roots [47,48].…”

Modeling growth, development and yield of cassava: A review

“…However, a recent overview of cassava physiology indicated that the maximum crop growth rates for cassava at LAI > 4 is relatively constant at around 22−24 g m −1 d −1 over a wide range of conditions and is less than that of other crops with similar photosynthetic rates ( Cock and Connor, 2021 ). This almost constant maximum crop growth rate fits with the observations that during periods of high solar radiation photosynthesis of cassava is restricted by VPD rather than solar radiation ( Vongcharoen et al, 2019 ). Thus, crop growth rate as a function of LAI, if corrected for temperature and soil water stress, may serendipitously incorporate the combined effects of VPD and solar radiation.…”

Physiology, Growth and Yield of Different Cassava Genotypes Planted in Upland with Dry Environment during High Storage Root Accumulation Stage

“…The same leaves were then preadapted to a dark period for one hour by fixing special tags on each leaf blade before measurements were retaken. After one hour of dark adaptation, the sensor cup was fitted on the leaf for measurement of maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) [12,14,[18][19][20][21]. Relative water content (RWC) for those the same leaves as Pn and chlorophyll fluorescence evaluations were recorded between 9.00-10.00 a.m., where 1 cm 2 in leaf area was collected using a leaf disc borer.…”