青海豌豆根腐病病原菌种类及致病性的研究

豌豆极腐病是青海东部干旱地区豌豆生产上的一种新病害,近年来危害逐年加重,致使豌豆产量遭受严重损失。根据分离鉴定和致病性测定结果,青海豌豆根腐病病原真菌是由茄镰刀菌、尖孢镰刀菌、豌豆丝囊霉、根串珠霉、立枯丝核菌、腐霉、链孢粘帚霉等复合反染所引起的。经回接试验：镰刀菌和豌豆丝囊霉对豌豆具有较强的致病力;腐霉及其他病原菌则有加强腐烂作用。     

BROWN ROOT ROT OF TOMATOES

Population counts and nutritional grouping of bacteria from a tomato-sick soil showed that steaming greatly reduced the population and the percentage of group I bacteria (i.e. those able to use inorganic nitrogen). The numbers subsequently increased, and by the time tomatoes were planted, the distribution of nutritional groups approximated to that in unsteamed soil. Rhizosphere and root-surface population numbers did not differ widely in steamed and unsteamed soils. The nutritional groups in soil before planting differed much more between samples from steamed soil with a changing population, than from soil unsteamed for 3 years. Groups I and II (bacteria requiring amino acids) were higher in unsteamed, cropped soil than in steamed soil, and were dominant in rhizosphere and root-surface populations. Group I increased on the root surface in unsteamed soil from July to October, whereas group II increased on root surfaces in steamed soil. Group V (bacteria requiring soil extract) was less frequent on the root surface than in soil from plots unsteamed for 1 year, but more frequent on the root surface than in soil unsteamed for 3 years.     

BROWN ROOT ROT OF TOMATOES

Tomato roots with brown root rot showed three types of lesion: cortical rot of fine roots, 'corky root', and basal stem rot. The fungi most commonly isocated from diseased roots were: Colletotrichum atramentarium, Chaetomium spp., Cephalosporium spp., Volutella ciliata , and a grey mycelial fungus sometimes producing pycnidia ( Pyrenochaeta sp.). Other fungi isocated less frequently were: Myrothecium roridum, Petriella asymmetrica, Trichoderma airide, Phytophthora spp., Alternaria sp. and Fusarium spp. There were differences between the numbers of each species isocated from the three types of lesion in steamed and in unsteamed soils, and some seasonal variation.
Inoculation experiments with seedlings in vitro showed that Ckaetomium cochliodes and Petriella asymmetrica could infect radicles. On older plants growing in soil Colletotrichum atramentarium was the only effective pathogen. Culture filtrates from C. atramentarium, Chaetomium cochliodes , and P. asymmetrica decreased root growth when tested in vitro. Leachates from loam and a loam-manure mixture decreased the growth of tomato root-tip cultures; the effect of these leachates was altered by autoclaving.