Seasonal Variation in Canopy Size, Light Penetration and Photosynthesis of Three Cassava Genotypes with Different Canopy Architectures

Abstract

The objective of this study was to investigate the effect of canopy size (CS) on light penetration and leaf photosynthesis of three cassava genotypes (Kasetsart 50 (KU50), Rayong 11 and CMR38-125-77) under two planting dates in two years. Data were recorded for CS, leaf area index (LAI), leaf photosynthesis, biomass (BM), storage root yield (SRY), starch content (SC) and harvest index (HI). The variation of CS depended on temperature, solar radiation (SR), relative humidity (RH) and day length (DL). In early growth stages, the crops planted in May had higher CS than the crops planted in November, because they were subjected to higher temperature, more SR, higher RH and longer DL. In contrast, the storage root accumulation of the crops planted in November was under better climatic factors than the crops planted in May. Therefore, the crops planted in November had higher BM and SRY than the crops planted in May for KU50 and CMR38-125-77. However, Rayong 11 in the May planting date maintained higher CS during storage root accumulation than the other genotypes, and BM and SRY of Rayong 11 were not different for the two planting dates in both years. KU50 and CMR38-125-77 had higher BM and SRY in the November planting, whereas in the May planting, the SRY and BM of the three genotypes were not significantly different. Genotypes that maintained high CS at the storage root accumulation stage could be indirectly selected for high BM and SRY in cassava breeding programs.

Canopy Structure and Photosynthetic Performance of Irrigated Cassava Genotypes Growing in Different Seasons in a Tropical Savanna Climate

“…For cassava planted in June (Rainy PD) and December (Cool PD2), at 3MAP, CMR38-125-77 had the highest LAI (Table 1), which corresponded to its lowest percent light penetration (Figure 3), and therefore high light interception by leaves at the upper canopy levels. Similar findings were reported for cassava planted in May 2016 (rainy season) and November 2015 (cool season), LAI of the 3MAP plants were higher in CMR38-125-77 than Rayong 11 and Kasetsart 50 [30]. Moreover, for the Rainy PD, CMR38-125-77 recorded the highest Pn at five canopy levels, and for the Cool PD2, it showed the highest Pn at three canopy levels, resulting in the highest mean Pn (Table S2).…”

“…Earlier work reported that from 4MAP to 5MAP, cassava generally attained an LAI of around 3.0 when the plants received 90% light interception [79] and the plants should reach the maximum LAI of 3.0-3.5 m 2 m −2 as quickly as possible to obtain optimum yield [12,27]. However, more recent research using improved high-yielding cultivars growing in well-watered fields in tropical savanna climate reported higher LAI values between 4.0 to 5.0 m 2 m −2 at 5MAP to 6MAP [30,80]. In this study, the canopy structures of cassava plants at 6MAP planted in different seasons showed more variation than those observed at 3MAP (Table 1).…”

“…Therefore, there are less carbon sources for leaves to maintain physiological status of the actively photosynthesizing leaves. This could result in a low net photosynthesis rate of the 6MAP plants compared with the 3MAP plants [30,38]. During the early growth stage up to 3MAP (when most photoassimilates are partitioned to accelerate leaf growth to obtain a close canopy and high biomass), the desirable canopy traits related to high photosynthetic performance would be the ones contributing to relatively high LAI values.…”

“…The mature plant generally takes one of two forms: either spreading stems (forking) or erect stems (non-forking) [27]. The forking of cassava affects the canopy development, yield, and dry matter partitioning and is related to increases in the LAI and yield [28][29][30]. The LAI values for the high storage root yields of cassava was reported at 3-3.5 m 2 m −2 , while leaf abscission began at LAI of 5.0-6.0 m 2 m −2 [12,31].…”

“…Photon flux density at different levels in a canopy or position on a live crown is often the major factor determining the rate of CO 2 assimilation of individual leaves [33][34][35][36]. Net photosynthesis rate (Pn), maximum net photosynthesis (Pn (Imax) ), dark respiration (RD), and light compensation point (I comp ) of the lower canopy leaves of cassava were much reduced compared to those of the upper-position leaves [30,37,38]. Sun and shade types of leaves develop respective types of photosynthetic pigment, which helps plants to perform photosynthesis and survive under adverse conditions [39][40][41].…”