A new approach to evaluate relative resistance and tolerance of tomato cultivars to begomoviruses causing the tomato yellow leaf curl disease in Spain

A simple procedure to evaluate relative resistance and tolerance of tomato cultivars to the begomoviruses causing tomato yellow leaf curl (TYLC) disease in Spain was developed. To estimate the resistance and tolerance levels of a cultivar, several formulae were developed based on the ratio of infected plants, virus titre (estimated by tissue–print hybridization) and symptom intensity. The formulae were applied to five commercial tomato cultivars (Amoretto, Birloque, Royesta, Tovigreen and Ulises) naturally infected by TYLC viruses. The analyses showed that Ulises, Birloque and Tovigreen exhibited a moderate resistance, and Ulises was also highly tolerant. There was a positive correlation between symptom intensity and virus titre in infected plants, suggesting that the hybridization technique could also be used as an early estimator of tolerance. Finally, molecular hybridization and nucleotide sequence analyses of the begomovirus intergenic region showed that the local TYLC virus population consisted of a single species, Tomato yellow leaf curl virus (TYLCV, formerly TYLCV-Israel), with low genetic variation (nucleotide identity between isolates higher than 97%).     

黑杨萎蔫枝叶对棉铃虫生殖行为的影响

研究了黑杨(Populus nigra)萎蔫枝叶及其气味对棉铃虫成虫的隐藏部位、产卵部位、交配率及产卵量等的影响，并对黑杨萎蔫枝把在田间诱集到的棉铃虫雌蛾进行了解剖观察。结果表明，在田间，黑杨萎蔫枝把诱集到的棉铃虫93．3％已经交配。在气候箱中，放置黑杨萎蔫枝叶的环境中配对饲养的棉铃虫，经过1个暗期和2个暗期后，其交配率与对照环境中的均无显著差异。在光期开始时，有51．5％的成虫隐藏在饲养笼内所设置的黑杨叶子圆片下，对照纱布圆片下仅有16．7％。叶子圆片所在区域的日平均落卵量显著大于对照区。黑杨萎蔫枝叶及其气味对棉铃虫的产卵前期、产卵持续期、成虫寿命和产下50％的卵所用的时间无显著影响，但饲养笼内有黑杨枝把或黑杨叶片气味存在时，棉铃虫的产卵量比模拟枝把和对照显著提高。     

新疆美洲斑潜蝇寄主种类及适合度的调查

通过乌鲁木齐、昌吉等地调查，发现新疆美洲斑潜蝇的寄主植物计有17科55种，其中蔬菜28种(变种)、大田作物8种，花卉和草坪植物13种、野生植物6种。以豆科、葫芦科植物受害最重。应用欧氏距离法的系统聚类分析，研究了美洲斑潜蝇对14种常见寄主植物的适合度；将其划分为5个类型，即最优适宜寄主、良好适宜寄主、适宜寄主、稍次适宜寄主和非适宜寄主。为害虫的防治决策提供了科学依据。     

膨胀素在果实完熟中的作用

 概述了细胞壁蛋白质膨胀素(Expansin)的发现、作用机制、基因家族、功能和研究现状。重点论述了膨胀素在果实完熟中的作用及其与细胞壁酶之间的相互关系，提出了利用转基因技术调节果实完熟和软化的新策略。关键词：中图分类号：     

烯效唑浸种对黄瓜的壮苗效应

研究不同浓度烯效唑浸种对黄瓜幼苗生长发育的影响。结果表明,烯效唑可抑制黄瓜幼苗徒长,使株高降低,比叶重增加,根冠比和壮苗指数增大,叶绿素含量增加,根系活性增强,在形态上和生理上表现出显著的壮苗效应;烯效唑对黄瓜有极显著的增产作用,以20 mg·kg-1处理最佳,促进增产的主要原因是提高了单株结瓜数。     

Preliminary investigation of the causal agent(s) of a disease causing leaf curl of tobacco in South Africa

A high incidence (86%) of potyvirus infection was noted in tobacco plants exhibiting a form of leaf curl in South Africa. Despite leaf curl being reported in the literature to be of geminiviral aetiology, no geminiviruses were detected. Furthermore, no other virus particles were detected by virus purification, TEM and serology. Twelve species of dsRNA were consistently isolated from these tobacco plants, but were absent from other forms of leaf curl-affected and healthy tobacco. Aphid and mechanical inoculation demonstrated that the purified potyvirus(es) did not cause leaf curl symptoms, but rather mild mottle and mosaic symptoms in tobacco. Partial characterization of the potyvirus preparation showed a possible relationship to a South African strain of potato virus Y. Because potyvirus-inoculated plants did not manifest leaf curl symptoms, and because leaf curl symptoms were noted in some plants not infected with a potyvirus, it was concluded that the potyvirus is not involved in the leaf curl aetiology, but causes a latent infection, the symptoms of which are masked. The pattern of the dsRNA banding, induction of enations and lack of mechanical and seed transmission are common to plant reoviruses. The possibility of a phytoreovirus involvement in this form of leaf curl is currently being investigated. The results from this study suggest that tobacco leaf curl disease worldwide, with regard to geminiviruses, be re-evaluated.     

The effect of solar heating of soil on natural and inoculated agrobacteria

Solarization trials were carried out over 3 years and in two countries to control crown gall disease on fruit trees and eliminate Agrobacterium . In 1992, agrobacteria in naturally infested soils of two Italian nurseries were monitored before and after solarization. Agrobacteria populations decreased by 99% and 92% after the treatment; however, crown gall incidence did not decrease. In 1993 and 1994 solarization was tested in Oregon in fields artificially infested with two marked strains of A. tumefaciens . In sandy loam soil, the target bacteria were eliminated in 4 weeks, while in silty clay soil the populations were markedly reduced after 2 months of treatment. Crown gall incidence on cherry rootstocks transplanted to the field at the end of 1993 was 3.7% in the sandy loam soil control plots, while no tumours were observed on plants from solarized plots. The use of solarization in combination with reduced doses of metham-sodium was also evaluated.     

Transmission of grapevine leafroll-associated closteroviruses by Pseudococcus longispinus and P. calceolariae

The transmission of two closteroviruses associated with grapevine leafroll, GLRaV-1 and GLRaV-3, from grapevine to grapevine by the mealybugs, Pseudococcus longispinus and P. calceolariae (Homoptera: Pseudococcidae) was studied. Controlled transmission experiments using the first and third instars of each insect were conducted twice during the 1993–94 growing season to investigate the consequence of virus accumulation within the donor vine leaf tissue on the incidence of virus transmission to healthy recipient vines. Transmission of GLRaV-1 and GLRaV-3 was determined by ELISA testing recipient vines in July 1994 and March 1995. GLRaV-3 was transmitted to recipient vines by P. longispinus and P. calceolariae first instars only. An increase in virus titre within the season did not significantly alter the transmission rate of GLRaV-3 by either P. longispinus or P. calceolariae first instars. P. longispinus and P. calceolariae failed to transmit GLRaV-1 to recipient vines.