Influence of crop rotation and intercropping of cassava with legumes on VA mycorrhizal symbiosis of cassava

Summary In comparison to cassava grown in monoculture the root infection of cassava with vesicular-arbuscular mycorrhiza was increased by crop rotation with grain legumes in the field. This was also found when cassava was intercropped with legumes and fertilized. A possible specificity of mycorrhizal fungi to increase the yield of one species more than the other when grown in association, is discussed.     

Enzyme activities in a clay-loam soil amended with various crop residues

Summary Amylase, dehydrogenase, arylsulphatase and phosphatases activities were measured in a clay-loam soil amended with seven different crop residues. All enzyme activities, except phosphomonoesterase, were generally higher in the derived soil samples than in the original soil. Addition of tobacco and sunflower residues caused an increase on most of the enzyme activities while tomato residues increased only the amylase and phosphodiesterase activities. As the enzyme activities were positively correlated to each other, a common source of the enzymes is suggested even though the coefficients of correlation demonstrate that only a low percentage of the variability can be ascribed to the interactions among enzyme activities.     

Redistribution of nitrogen in an ecosystem due to long-term fertilization and continuous cropping

Summary When a leguminous crop like cowpea was included in a crop rotation of Ganga 5 maize, CO 7 ragi and CO 2 cowpea, the total nitrogen content in the soil was considerably increased even in the unfertilized plots. The leguminous crop fixed atmospheric nitrogen at the rate of 205 kg N/hectare/year. Potassium did not influence the status whereas phosphorus, over a background of N, improved it. Considerable quantity of N fixed was observed to have been redistributed in the soil which depended on the fertilization pattern.     

Effect of salinity on quality of various agricultural crops

Summary The effect of salinity on the quality of various agricultural crops has not yet been explored much. This information is very important to Israel due to the increasing use of saline water for irrigation. This paper reports the effect of saline irrigation water on the quality, especially the taste, of several crops. Fruits from a processing tomato cultivar exposed to various degrees of salinity had higher values for total soluble solids (TSS) and acidity than their controls. The yield of fruit after saline water irrigation is lower, but this is offset by the nigher fruit quality and its consequent higher value. Melon fruits from plants subjected to saline water scored higher in taste than their controls when the fruits were analyzed fresh. After 3–4 weeks of storage at room temperature, there was no longer any difference in taste. Even though salinity slightly increased the TSS content, this did not correlate with the taste scores. Iceberg lettuce grown with saline water did not significantly differ in taste from its control, even when the sensitive triangle taste test was used. The same was true for peanuts. Thus, for these two crops no advantage of better quality would compensate for possible lower yields. Salinity had little effect on the yield of two varieties of Chinese cabbage, but increased the frequency of tipburn.     

Effects of agricultural cropping systems on micronutrients transformation

Summary The effect of cropping systems of wheat-maize (WM), wheat-rice (WR), wheat-groundnut (WG), gram-bajra (GrB), potato-guara (PGu), and raya-mash (RaMa) in combination with treatments of dummy (uncultivated area) and applied Zn 0.0 (Zn₀), 2.8 (Zn₁), 5.6 (Zn₂) 11.2 (Zn₃) kg/ha was studied on the transformation of labile Zn fractions: exchangeable (Exch.), adsorbed (TAd) [weakly (WAd), moderately (MAd), strongly (SAd)], and organic matter (OM) in different layers of sandy loam soil. The added Zn stayed largely in the 0–30 cm layer and was associated with the WAd- and OM-Zn fractions. About 70% of the total labile Zn (PAv) remained in the WAd- and OM-Zn, that is, 33 and 39% in 0–15 cm layer, and 33–39% and 31–36% in 16–150 cm layer. All the Zn fractions in 0–15 cm layer, and only of WAd in 16–30 cm layer, significantly increased with rates of Zn addition. These were also significantly higher in Zn_1–3 than Zn₀ and dummy treatments because of the residual Zn. Diverse effects of cropping systems on soil properties, residual Zn, and labile Zn fractions were found. The influence was strong in 0–15 cm layer decreasing gradually with soil depth due largely to differences in Zn requirement, crop intake of various Zn fractions and the cultural practices of the systems. All the crops and rotations appreciabilly responded to Zn application. Uptake of Zn by crops markedly and successively increased with increasing rates of Zn application. The WR caused a significant increase in soil organic matter whereas WR and WM in CaCO₃. The WR, WM and GrB resulted in a decrease in pH while WG and GrB in CaCO₃. The RaMa and PGu maintained much higher residual Zn than other systems. The systems which caused the maximum decrease in Zn fractions were: cereal-cereal (WM) in Exch. legume-millet (GrB) in all the adsorbed, PAv and the Zn associated with CaCO₃, vegetable-legume (PGu) also in MAd and SAd; and cereal-legume (WG) in OM and PAv. Hence GrB, WG and WM in that order will cause the deficiency of Zn much earlier than the other systems due to greater use and or transformation of WAd- andOM-Zn. Such effects were least under RaMa because it increased the WAd-, MAd- and OM-Zn.     

γ-Lactam-Based Antifungal Compounds against the Wheat Pathogen Zymoseptoria tritici

As new environmentally friendly and effective antifungal agents are deeply needed, efficient ecofriendly strategies were designed to access two series of compounds inspired from natural γ-lactams. Designed compounds were fully characterized and evaluated as antifungal candidates against Zymoseptoria tritici, the main pathogen on wheat crops. The targeted derivatives were prepared from natural resources using green solvents, simple procedures, and limited purification steps. These bio-inspired compounds revealed as good candidates for further development of efficient crop protection products. Indeed, the HIT compounds exhibited IC₅₀ around 1 μg/mL and were more active than the references tebuconazole and bixafen towards some multidrug-resistant strains. Two dozen of derivatives have been obtained for each series and allowed to establish early structure-activity relationships useful for the development of next generation of γ-lactam derivatives with improved efficacy.     

Citrus orchard evapotranspiration: Comparison between eddy covariance measurements and the FAO-56 approach estimates

Abstract

The aim of this study was to use the FAO-56 single and dual crop coefficient approaches to estimate actual evapotranspiration (ET_a) over an irrigated citrus orchard under drip and flood irrigations in Marrakech, Morocco. The results showed that, by using crop coefficients suggested in the FAO-56 paper, the performance of both approaches was poor for two irrigation treatments. The Root Mean Squared Error (RMSE) between measured and simulated ET_a values over the citrus orchard under drip irrigation was about 1.43 and 1.27 mm/day for the single and dual approaches, respectively, while the corresponding statistics for the orchard irrigated by the flooding technique was 1.87 and 2.48 mm/day. After determination of the appropriate values of the crop coefficient (K_c) based on eddy covariance measurements of ET_a, the performance of both approaches greatly improved. The obtained K_c values were lower than the FAO-56 values by about 20%. The low K_c values obtained reflect the practice of drip irrigation for one field and the low value of cover fraction for the other field. Additionally, the efficiency of the irrigation practices was investigated by comparing the measured K_c for two fields. The results showed that a considerable amount of water was lost by direct soil evaporation from the citrus orchard irrigated by flooding technique.     

代谢基因工程提高作物产量的分子靶标

应用基因工程技术对植物细胞内的代谢途径进行遗传修饰,已成功地使细胞代谢发生改变或合成新的化合物。光合作用,淀粉合成,氮素同化和水分利用等是形成作物产量的基础代谢。对这些代谢途径中的关键步骤和靶分子进行基因修饰以提高作物产量的研究已取得长足的进展,并正在发展成为提高作物产量的新途径。本文着重论述应用代谢基因工程提高作物产量的技术策略,研究现状,存在的问题,所面临的挑战和应用前景。     

作物种质资源的价值及其评估

回顾了对作物种质资源价值的认识过程,对作物种质资源价值评估的理论和方法进行了论述,指出了作物种质资源价值评估及其产权保护的必要性,对作物种质资源价值评估一些问题和难点进行了探讨,并对今后研究提出了建议.     

Histopathological studies of sclerotia of phytopathogenic fungi parasitized by a GFP transformed Trichoderma virens antagonistic strain

The gfp gene from the jellyfish Aequorea victoria, coding for the Green Fluorescent Protein (GFP), was used as a reporter gene to transform a Trichoderma virens strain I10, characterized as having a promising biocontrol activity against a large number of phytopathogenic fungi. On the basis of molecular and biological results, a stable GFP transformant was selected for further experiments. In order to evaluate the effects of GFP transformation on mycoparasitic ability of T. virens I10, sclerotia of Sclerotium rolfsii, Sclerotinia sclerotiorum and S. minor were inoculated with the T. virens strain I10 GFP transformant or the wild type strain. Statistical analysis of percentages of decayed sclerotia showed that the transformation of the antagonistic isolate with the GFP reporter gene did not modify mycoparasitic activity against sclerotia. Sclerotium colonization was followed by fluorescent microscopy revealing intracellular growth of the antagonist in the cortex (S. rolfsii) and inter-cellular growth in the medulla (S. rolfsii, and S. sclerotiorum). The uniformly distributed mycelium of T. virens just beneath the rind of sclerotia of both S. rolfsii and S. sclerotiorum suggests that the sclerotia became infected at numerous randomly distributed locations without any preferential point of entry.