Effect of Plant Density on the Yield of Hydroponically Grown Heat-Tolerant Tomato under Summer Temperature Conditions

Producing enough tomato to meet market demand sustainably has not been feasible in the tropics like Ghana. Attempts to improve production using greenhouse facilities have not addressed the challenge because of high-temperature conditions in the greenhouse, which are difficult to manage. Heat stress, arising from high temperatures, hinder the performance of tomato in terms of fruit set and yield. Moreover, the impending climate change is expected to impose more unfavorable environmental conditions on crop production. An experiment was conducted in (greenhouse at Chiba University, Japan) summer period, which has similar high-temperature conditions like Ghana. This work sought to increase the yield of a heat-tolerant tomato using a state-of-the-art hydroponic system through high-density planting. The outcome of this work was intended for adoption and practice in Ghana. A Heat-tolerant tomato “Nkansah HT” along with Lebombo and Jaguar cultivars, were grown at high and low plant densities (4.1 and 2.7 plants m-2 respectively). Each plant was grown in a low substrate volume culture (0.5 L plant-1) in a recirculating nutrient film technique (NFT) hydroponic system. Parameters measured were plant growth and dry matter assimilation at 12 weeks after transplanting, and the generative components. Results showed that a high plant density increased plant height but reduced chlorophyll content by 9.6%. Under temperature stress conditions, the three cultivars recorded more than 95% fruit set, but plant density did not affect the fruit set and the incidence of blossom end rot (BER). The incidence of BER reduced the marketable yield of the Jaguar cultivar by 51% but, this physiological disorder was not recorded in the HT and the Lebombo cultivars. A high-density planting increased the yield per unit area increased by 38.9%. However, it is uneconomical to cultivate the Jaguar cultivar under a heat stress condition due to its high susceptibility to blossom end rot. To improve the yield of tomatoes under tropical heat stress with a threatening climate change condition, the HT is a better cultivar suited for high-density planting. This study shows that high-density cultivation of the HT cultivar in NFT hydroponic system has the potential to increase Ghana’s current tomato yield by 4.8 times.

The causes and impacts for heat stress in spring maize during grain filling in the North China Plain--A review

High-temperature stress （HTS） at the grain-filling stage in spring maize （Zea mays L.） is the main obstacle to increasing productivity in the North China Plain （NCP）. To solve this problem, the physiological mechanisms of HTS, and its causes and impacts, must be understood. The HTS threshold of the duration and rate in grain filling, photosynthetic characteristics （e.g., the thermal stability of thylakoid membrane, chlorophyll and electron transfer, photosynthetic carbon assimilation）, water status （e.g., leaf water potential, turgor and leaf relative water content） and signal transduction in maize are reviewed. The HTS threshold for spring maize is highly desirable to be appraised to prevent damages by unfavorable temperatures during grain filling in this region. HTS has negative impacts on maize photosynthesis by damaging the stability of the thylakoid membrane structure and degrading chlorophyll, which reduces light energy absorption, transfer and photosynthetic carbon assimilation. In addition, photosynthesis can be deleteriously affected due to inhibited root growth under HTS in which plants decrease their water-absorbing capacity, leaf water potential, turgor, leaf relative water content, and stomatal conductance. Inhibited photosynthesis decrease the supply of photosynthates to the grain, leading to falling of kernel weight and even grain yield. However, maize does not respond passively to HTS. The plant transduces the abscisic acid （ABA） signal to express heat shock proteins （HSPs）, which are molecular chaperones that participate in protein refolding and degradation caused by HTS. HSPs stabilize target protein configurations and indirectly improve thylakoid membrane structure stability, light energy absorption and passing, electron transport, and fixed carbon assimilation, leading to improved photosynthesis. ABA also induces stomatal closure to maintain a good water status for photosynthesis. Based on understanding of such mechanisms, strategies for alleviating HTS at the grain-filling stage in spring maize are summarized. Eight strategies have the potential to improve the ability of spring maize to avoid or tolerate HTS in this study, e.g., adjusting sowing date to avoid HTS, breeding heat-tolerance varieties, and tillage methods, optimizing irrigation, heat acclimation, regulating chemicals, nutritional management, and planting geometric design to tolerate HTS. Based on the single technology breakthrough, a com- prehensive integrated technical system is needed to improve heat tolerance and increase the spring maize yield in the NCP.

Improvement of heat－tolerance by training I．Evaluation of effects of long－distance running and march training on heat－toleran

in order to verify the heat-tolerance effect, two trainings, 90 min marching with load (WBGT 24. 6～35.6℃) and 10 km running (WBGT 25.0～31.1℃) were performed in laboratory and field under hot climate.Ten to twelve times (days) of training were carried out

Improvement of heat－tolerance by training Ⅱ．Evaluation of effects of cross－country race and heat－bath training on heat－tolera

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