Abstract
ABSTRACTWater deficit stress is a major factor that inhibits the overall growth and development in cassava (Manihot esculenta), leading to decreased storage root yield. We conducted a study to investigate whether thermal sensing could be used to indicate water deficit stress and the health and yield of cassava crops in field. The objective of the study was to use thermal imaging to determine relationship between crop water stress index (CWSI) and physiological changes, and to identify the critical CWSI point in fields of cassava cv. Rayong 9 under well-irrigated and water-deficit conditions. At the time of storage root initiation (85 DAP [day after planting]), thermal imagery was collected and the physiological changes and growth characters were measured prior to storage root harvesting (162 DAP). Thermal infrared imager was used to measure the canopy temperature and CWSI of cassava plants. Net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rates (Tr) of cassava plants under water deficit conditions for 29 d (114 DAP) were significantly decreased, leading to delayed plant growth as compared to those under well-irrigated conditions. In contrast, air vapor pressure deficit (VPDair) and CWSI in drought-stressed plants were higher than well irrigated plants. High correlations between Tr/gs/Pn and CWSI were observed. The study concludes that CWSI is a sensitive indicator of water deficit stress caused due to stomatal function.Abbreviations: CWSI: crop water stress index; DAP: day after planting; Pn: net photosynthetic rate; gs: stomatal conductance; Tr: transpiration rate; VPDair: air vapor pressure; RMSE: root mean square error
Highlights
Cassava (Manihot esculenta Crantz; Euphorbiaceae), a perennial crop, is one of the most important staple foods in the tropical countries and considered as the fourth most important source of energy (Balagopalan, 2002)
Sprinkle irrigation was used for well-watered plots (WW) when the tensiometer was less than −30 kPa to maintain the soil water potential
Soil moisture in the well-watered plots (WW) was maintained, whereas it was declined in the water-stressed plots (WS) (Figure 2(f))
Summary
Cassava (Manihot esculenta Crantz; Euphorbiaceae), a perennial crop, is one of the most important staple foods in the tropical countries and considered as the fourth most important source of energy (Balagopalan, 2002). It is classified as a drought tolerant crop, the growth characters and yield performances decline under prolonged dry periods (El-Sharkawy, 2004). Reduction in the storage root yield depends on the duration of the water deficit conditions and the growth stage of the storage root (El-Sharkawy, 2006). The critical period of cassava cultivation that could be affected by water deficit conditions ranges from 1 to 5 months after plantation (MAP), identified as the root initiation and tuberization stages (El-Sharkawy, 2007). Continuous water deficit for at least 2 months during this period can reduce storage root yield by 32–60% (Hillocks, Thresh, & Bellotti, 2002). In response to prolonged water stress, reduced shoot biomass and storage root were observed in cassava with significant reduction during early water stress period (2–6 MAP) (El-Sharkawy, 2012). The stomata rapidly close as the leaf water potential decreases, the vapor pressure deficiency increases and both rate of photosynthesis and transpiration decrease (Hillocks et al, 2002)
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