The Potential Use of Metamitron as a Chemical Fruit-thinning Agent in Mandarin

Under conditions of profuse flowering and excessive fruit set, citrus (Citrus sp.) fruit need to be thinned to increase the size of remaining fruit, reduce the intensity of alternate bearing, or both. Metamitron was recently developed as a chemical fruit-thinning agent for apple (Malus ×domestica) and pear (Pyrus communis), and it inhibits photosynthesis and is thought to transiently reduce the carbohydrate pool in fruit trees. Citrus trees are sensitive to carbohydrate stress during and immediately after flowering, but the response of citrus to foliar treatment with a photosynthesis inhibitor, such as metamitron, is unknown. The purpose of this study was to evaluate metamitron for its effects on leaf carbohydrates and its ability to chemically thin citrus fruitlets. Significant fruit-thinning effects were found in all the experiments conducted over two seasons. A 300 mg·L−1 metamitron treatment reduced leaf sugars and leaf total carbohydrates, and consistently reduced the total number of fruit per tree in both seasons in ‘Nadorcott’ mandarin (Citrus reticulata), irrespective of the timing of application. In the second season, a reduction in fruit yield was reported with an increase in metamitron concentration, both in mass and number of fruit per tree. A 150 mg·L−1 metamitron treatment in November had no fruit-thinning effects, and fruit yield was not different from the control. The application of metamitron did not increase the fruit size of ‘Nadorcott’ mandarin and had no direct effect on other fruit quality attributes in either season. Metamitron can be used as a chemical fruit-thinning agent to reduce fruit numbers in ‘Nadorcott’ mandarin, but an increase in fruit size or quality should not be expected.

Mycorrhizal Fungi Regulate Root Responses and Leaf Physiological Activities in Trifoliate Orange

Plant responses to mycorrhization are mediated through secretion of certain signal molecules deposited in mycorrhizosphere in response to environmental stimuli. Responses of four arbuscular mycorrhizal fungi (AMF), namely Claroideoglomus etunicatum, Diversispora versiformis, Funneliformis mosseae, and Rhizoglomus intraradices on root morphology, lateral root (LR) number, and leaf carbohydrates, nitric oxide (NO), and calmodulin (CaM) changes were studied using trifoliate orange. Inoculation response of D. versiformis, F. mosseae, and R. intraradices registered significantly higher plant growth performance (plant height, stem diameter, leaf number, and shoot and root biomass), root morphological traits (total length, projected area, surface area, and volume), and LR number (first-, second-, third-, and forth-order), compared to un-inoculated response. Higher concentrations of CaM, NO, glucose, and fructose and lower sucrose level in leaves were observed in AMF-seedlings than in non-AMF seedlings. Correlation studies further revealed, root morphological traits and LR numbers were significantly negatively correlated with sucrose whereas positively correlated with glucose, fructose, NO, and CaM level in leaves. These results suggested, AMF-induced root modification is routed through sucrose cleavage and partly through changes in NO and CaM.

Water relations in physic nut according to climatic seasonality, in semiarid conditions

The objective of this work was to determine the effect of climatic seasonality on physic nut (Jatropha curcas), in field, under semiarid climate conditions. Stomatal conductance (g s), transpiration (E), soluble leaf carbohydrates (SLC), free amino acids (FAA) and total proteins (TP) were measured in leaves, in a commercial plantation in Northeast Brazil, during the summer and autumn. Plants showed high g s and E, as well as SLC, FAA and TP contents in the summer, which gradually decreased with the lower temperatures and photosynthetically active radiation during the autumn, despite the higher water availability. Even in conditions of adequate water availability, the combination of low temperatures and reduced light drastically decreased foliar metabolism.