A field experiment was conducted with two cassava cultivars and eight levels of nitrogen to examine the relationship between extractable chlorophyll (Chl) content of cassava leaves and both the Chl meter value (SPAD) and leaf colour chart (LCC) score. The SPAD, LCC, and Chl a+b content were influenced by leaf position, growth stage, cultivar (cv.), and N fertilization. The cvs. and N fertilization had significant effect on SPAD, LCC, and Chl a+b content of youngest fully expanded leaf (leaf 1) blade in most cases. An F-test indicated that common equations pooled across cvs., N fertilization, and growth stages could be used to describe the relationships between Chl a+b content and LCC and between SPAD and LCC, but not between SPAD and Chl a+b content. Relationships between tuber yield and SPAD, LCC, and Chl a+b content were significant (p<0.05) and positive at 30 and 60 d after planting. Thus LCC and SPAD can be used to estimate leaf Chl content which is an indicator of leaf N status. and M. Haripriya Anand, G. Byju.
Anticipating warming related to climate change, commercial mango plantations in China have been shifting from lower to higher elevations. Such a practice may expose mangoes to climatic conditions that could affect photosynthesis. Photosynthesis research on mango has previously examined mature plantations but exploring adequate functions before the time of fruit production is necessary for later crop success. Therefore, we established two main commercial mango cultivars, Tainong No. 1 and Jinhuang, at 450 m and 1,050 m and examined their photosynthetic performance. Our results showed that photosynthetic capacity parameters, including maximum photosynthetic rate, apparent quantum yield, maximum carboxylation rate, and photosynthetic electron transport rate, were significantly different between cultivars due to elevation and positively correlated with leaf nitrogen per area. Moreover, the seasonal gas exchange of the two cultivars showed variations due to elevation, particularly during the warmer seasons. Therefore, elevation affects the photosynthetic performance of these mango cultivars.
Field trials with a large group of cassava germplasm were conducted at the seasonally-dry and hot environments in southwest Colombia to investigate photosynthetic characteristics and production under drought conditions. Measurement of net photosynthetic rate (PN), photosynthetic nitrogen use efficiency (PNUE), mesophyll conductance to CO2 diffusion (g m), and phosphoenolpyruvate carboxylase (PEPC) activity of upper canopy leaves were made in the field. All photosynthetic characteristics were significantly correlated with final dry root yield (Yield). Correlations among the photosynthetic traits were also significant. PEPC activity was highly significantly correlated with PN and PNUE, indicating the importance of the enzyme in cassava photosynthesis and productivity. Among a small selected group from the preliminary trial for yield performance, the second year Yield was highly significantly correlated with PN measured on the first year crop. Thus variations in the measured photosynthetic traits are genetically controlled and underpin variations in yield. One short-stemmed cultivar M Col 2215 was selected for high root dry matter content, high harvest index, and tolerance to drought. It was tested under the semi-arid conditions of the west coast of Ecuador; participating farmers evaluated cultivar performance. This cultivar was adopted by farmers and officially released in 1992 under the name Portoviejo 650. and M. A. El-Sharkawy, Y. Lopez, L. M. Bernal.
In a growth chamber experiment, we determined net photosynthetic rate (PN) and leaf developmental characteristics of cultivars of a relatively small-, intermediate-, and a large-leaf genotype grown under irradiance of 450-500 µmol(photon) m-2 s-1 (HI), shade [140-160 µmol(photon) m-2 s-1] (LI), and after a shade-to-irradiation (LI >>HI) transfer. Differences in physiological responses of the genotypes were more pronounced in HI and LI>>HI plants than in LI plants. The small- and intermediate-leaf sizes had greater PN in the first measured leaf than the large-leaf type by 70 and 63 % in HI plants, and by 23 and 18 % in LI>>HI plants, respectively. Similar relationships were observed in the next developed leaf. The LI plants did not differ significantly in PN. Greater PN in the small- and intermediate-leaf size genotypes were not associated with greater total dry matter of the plant. Under irradiation, the large-leaf genotype accumulated more total nonstructural saccharides (TNS) and starch than the small- or intermediate-leaf size plants. TNS and starch concentrations in LI plants were about one-half those of HI and LI>>HI plants. These results should help to develop management practices that capitalize upon the competitive features of white clover in mixed-species swards. and D. P. Malinowski, D. P. Belesky, J. Fedders.