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  • Author or Editor: Suguru Sato x
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Global temperature increases are predicted over the next several decades. Earth surface temperatures in 1995 were the highest ever recorded. At day temperatures above 30C or night temperatures above 21C, tomato fruit production decreases. However, the temperature dependence of fruit production has not been described in terms of whether day temperatures, night temperatures, or mean temperatures are the most limiting. The process or tissue most sensitive to heat and most limiting to fruit production is also not known. The objectives of this experiment are to establish the temperature dependence of fruit set in tomatoes and to determine the importance of post-pollen production effects. We imposed a total of nine temperature treatments in a series of four separate experiments. Each experiment consisted of a 30/24C treatment and two other day/night temperature combinations with differing means and/or day/night temperature differentials. As mean daily temperature increased from 25 to 29C, fruit set, fruit number, total fruit weight, and seediness index (a quantitative rate of fruit seed content) declined. Temperature treatments did not affect average fruit weight. Higher mean temperatures promoted flowering except at the highest temperature. Mean temperature was more important than day/night temperature differentials or the specific daytime or nighttime temperature treatment.

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Peet et al. (1997) demonstrated that in male-sterile tomato plants (Lycopersicon esculentum L. Mill cv. NC8288) (MSs) provided with pollen from male-fertile plants (MFs) grown at 24°C daily mean, percent fruit set, total number and weight of fruit, and relative seediness decreased linearly as mean daily temperature rose from 25 to 29°C. The primary parameter affecting these variables was mean temperature, with day temperature at a given night temperature, night temperature at a given day temperature, and day/night temperature differential having secondary or no effect. To compare the effect of temperature stress experienced only by the female tissues with that experienced by the male tissues or both male and female tissues, MSs and MFs were grown in 28/22°C, 30/24°C, and 32/26°C day/night temperature chambers. Fruit yield and seed number per fruit declined sharply when increased temperatures were experienced by both male and female tissues (MFs). There was no fruit set in any of the MSs assigned to the 32/26°C pollen treatment, mostly because of the limited amount of pollen available from MFs. Both fruit production and seed content per fruit were also greatly reduced in MSs receiving pollen from 30/24°C grown MFs for the same reason. For plants experiencing stress only on female tissues (MSs grown at high temperatures, but receiving pollen from MFs grown at the lowest temperature), there was also a linear decrease in fruit yield as growth temperatures increased, as previously seen by Peet et al. (1997), but the temperature effect was less pronounced than that on pollen production. Thus, for this system, temperature stress decreased yield much more drastically when experienced by male reproductive tissues than when experienced only by female reproductive tissues.

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In nutrient film technique (NFT) vegetable production, the use of low-concentration nutrient solutions might lead to a nutrient concentration gradient along the bed, which can translate into nonuniform plant growth. The authors modified a conventional NFT system (cNFT) and propose a modified NFT (mNFT) that enables the production of lettuce (Lactuca sativa) plants of uniform fresh weight along elongated cultural beds. Two experiments were carried out to compare the systems when long cultural beds are used (18 m) in terms of uniformity of plant and nutrient solution characteristics. The results indicated that fresh weight of plants in cNFT decreased as the distance from the nutrient inlet increased, whereas no such trend was observed in mNFT. Leaf nitrate concentration in mNFT was uniform, whereas it was higher near the outlet of cNFT. Ascorbic acid concentration was also uniform in mNFT, but it was found to be lower near the outlet of cNFT. During Expt. 2, the oxygen content along the bed decreased from inlet to outlet in cNFT; however, in mNFT, it remained relatively constant at all sampling positions. Regarding the concentration of the nutrient solution along beds, no significant differences were found between inlet and outlet in both systems. It is suggested that the lower concentration of oxygen found at the outlet of cNFT might have reduced nutrient uptake, thus attenuating the difference in concentration between inlet and outlet. The temperatures of the nutrient solution along mNFT during Expt. 2 tended to be slightly lower than those of cNFT. However, temperatures were still too high and plant growth was negatively affected. The results of this study demonstrate that plants of uniform size and quality can be achieved in long cultural beds (up to 18 m long) supplied with a low-concentration fertilizer solution by using the proposed mNFT.

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