Simulation modelling of potato virus Y spread in relation to initial inoculum and vector activity

Potato virus Y(PVY) is a non-persistent virus that is transmitted by many aphid species and causes significant damage to potato production. We constructed a spatially-explicit model simulating PVY spread in a potato field and used it to investigate possible effects of transmission efficiency, initial inoculum levels, vector behavior, vector abundance, and timing of peak vector activity on PVY incidence at the end of a simulated growing season. Lower PVY incidence in planted seed resulted in lower virus infection at the end of the season. However, when populations of efficient PVY vectors were high, significant PVY spread occurred even when initial virus inoculum was low. Non-colonizing aphids were more important for PVY spread compared to colonizing aphids, particularly at high densities. An early-season peak in the numbers of noncolonizing aphids resulted in the highest number of infected plants in the end of the season, while mid-and late-season peaks caused relatively little virus spread. Our results highlight the importance of integrating different techniques to prevent the number of PVY-infected plants from exceeding economically acceptable levels instead of trying to control aphids within potato fields. Such management plans should be implemented very early in a growing season.     

试论小麦高蛋白育种

本文在引述国内外有关小麦蛋白质含量遗传研究进展的基础上,探讨了提高小麦蛋白质含量的育种途径：1)组配具有遗传多样性的杂交组合；2)通过远缘杂交创造优质新类型；3)人工诱变,打断基因间的不利连锁；4)通过无性系变异获得优质的变异体；5)优质基因转导；6)依据形态结构从现有品(系)种中鉴定筛选     

Weed species composition of small‐scale farmlands bears a strong crop‐related and environmental signature

Weed species loss due to intensive agricultural land use has raised the need to understand how traditional cropland management has sustained a diverse weed flora. We evaluated to what extent cultivation practices and environmental conditions affect the weed species composition of a small‐scale farmland mosaic in Central Transylvania (Romania). We recorded the abundance of weed species and 28 environmental, management and site context variables in 299 fields of maize, cereal and stubble. Using redundancy analysis, we revealed 22 variables with significant net effects, which explained 19.2% of the total variation in species composition. Cropland type had the most pronounced effect on weed composition with a clear distinction between cereal crops, cereal stubble and maize crops. Beyond these differences, the environmental context of croplands was a major driver of weed composition, with significant effects of geographic position, altitude, soil parameters (soil pH, texture, salt and humus content, CaCO₃, P₂O₅, K₂O, Na and Mg), as well as plot location (edge vs. core position) and surrounding habitat types (arable field, road margin, meadow, fallow, ditch). Performing a variation partitioning for the cropland types one by one, the environmental variables explained most of the variance compared with crop management. In contrast, when all sites were combined across different cropland types, the crop‐specific factors were more important in explaining variance in weed community composition.     

河西走廊夏型棉蚜为害损失与防治指标研究

棉蚜是甘肃棉区的优势害虫,主要是棉花成株期的夏型棉蚜（即伏蚜）对棉花造成为害。为探明河西走廊棉区棉花伏蚜的为害损失和防治指标,笔者于１９９５～１９９６年在甘肃敦煌和安西两地对其进行了初步研究。研究结果表明,棉株受伏蚜为害后主要是造成株高降低、蕾铃脱落率增加、吐絮数减少,铃重降低而减产。根据甘肃河西走廊棉区的棉花生产现状,提出棉田夏型棉蚜（伏蚜）的防治指标为平均单株３片叶蚜量５０头左右。