Biochemical and genetical studies on host-parasite relationship: Studies on the hydrolytic enzymes of two mutants of Fusarium vasinfectum ATK

Hydrolytic enzymes activities are studied in comparison in doubly virulent partial nicotinic acid requiring mutant and non-virulent para-aminobenzoic acid requiring mutant ofFusarium vasinfectum Atk. Protease, cellulase, amylase and lipase were found to be more active in the doubly virulent strain than the parent strain and para-aminobenzoic acid requiring mutant. Nucleases did not show any significant variations. In Vitro studies revealed that the enzyme activities are dependent on the total substrate available. Protease, Cellulase and Amylase are always extracellularly more active. Nucleases appear to be less active in mutants in comparison with parent strain. The significance of these points is discussed.This research has been financed in part by a grant made by the U. S. Dept. of Agricult. under P.L. 480.     

Mineral Uptake in Fusarium oxysporum f. sp. vasinfectum

A method for growing Fusarium oxysporum, a mycelial fungus, and a technique for its use in mineral uptake studies have been described. Some general characteristics of the uptake process were determined. The fungus, grown for 54 hours, was found to take up as much K as 15 to 20 meq/100 g dry weight in 2 to 4 hours from a solution of 5 meq/l KCl. Approximately 3 to 5 meq of this uptake was readily removed by a CaCl₂ rinse. The uptake was only slightly sensitive to pH over the range of 4 to 9. Below pH 4 uptake dropped rapidly. The age of the culture appeared to be the dominant factor in determining the rate of uptake. In contrast to other fungi, the presence of glucose during uptake was detrimental to K uptake. Conditions unfavorable for metabolic activity as low temperature, anaerobiosis, or the presence of DNP markedly reduced the uptake rate. Although the fungus took up Na from single salt solutions nearly as well as K, the latter ion was much preferred in mixtures of the two ions. The organism showed no significant metabolic uptake of Ca or Cl. During uptake from KCl solutions, the organic acid content increased. The increase, chiefly in succinic acid and to a lesser extent in acetic and citric acids, amounted to about half the K uptake. The remainder of the K taken up was correlated with a roughly equivalent efflux of cellular Mg.     

Lectins Specificity to Pathogenesis of Fusarium oxysporum f. sp. vasinfectum

Lectins of cotton were isolated from either resistant or susceptible seed cultivars. In agar-gel double diffusion tests, positive reactions took place between lectins of cotton cultivars and the antisera of their corresponding wilt Fusaria. The number of precipitin bands correlated with the degree of susceptibility of the tested cultivars. On the other hand, no visible reaction was detected when these antisera were subjected to react with either the resistant host or nonhost lectins.     

Interaction between Fusarium oxysporum F. vasinfectum and Cephalosporium maydis on cotton and maize

The interaction between Fusarium oxysporum (cause of cotton wilt) and Cephalosporium maydis (cause of maize late-wilt) on cotton roots is associated with an appreciable decrease in the severity of the cotton wilt disease. Reduction in infection is more pronounced when the latter fungus precedes the former in the soil than when they are inoculated simultaneously. C. maydis exerts little or no such effect when it follows F. oxysporum in the soil. C. maydis grows on the surface of cotton roots near growing points as a root-surface inhabitant. Dark red lesions are produced but these disappear, as does the fungus, when the root becomes hardened either naturally or in response to the growth of the fungus on the surface. The presence of the fungus is associated with increased production of root laterals. Cotton plants, including those which may appear healthy, show only mild internal symptoms of Fusarium infection when grown in soil inoculated with the two fungi, suggesting that the decreased severity of wilt is largely due to increased tolerance of the plants to infection with the disease as a result of increased number of root laterals. It is also possible that cotton roots with C. maydis on their surface become less suitable for the progress of F. oxysporum. F. oxysporum produces in culture a metabolite inhibitory to C. maydis. This may partly account for the little effect that the latter fungus exerts on the severity of wilt when it follows F. oxysporum in the soil. It appears that the interaction between F. oxysporum and C. maydis does not affect the pathogenicity of the latter fungus to maize.     

Studies on cellulase of the cotton wilt pathogen fusarium vasinfectum ATK

Cellulase of the cotton wilt pathogenFusarium vasinfectum was partially purified 19fold. The enzyme preparation had three pH optima at 5.4, 6.0 and between 8.0 and 8.4 and optimum temperature between 35 and 40°C. Irreversible denaturation of the enzyme resulted in 5 min below pH 1.5 and above 70°C. Thiol group inhibitors and EDTA inhibited the cellulase activity completely whereas reducing agents and metal ions Fe⁺⁺, Ca⁺⁺ and Cu⁺⁺ activated. The results are discussed in elation to pathogenicity towards the cotton plant.This research has been financed in part by a grant made by the United States Department of Agriculture, under P.L. 480.     

Interactions of Concomitant Species of Nematodes and Fusarium oxysporum f. sp. vasinfectum on Cotton

Meloidogyne incognita, Hoplolaintus galeatus, and North Carolina and Georgia populations of Belonolaimus longicaudatus were introduced singly and in various combinations with Fusarium oxysporum f. sp. vasinfectum on wilt-susceptible ''Rowden'' cotton. Of all the nematodes, the combination of the N. C. population of B. longicaudatus with Fusarium promoted greatest wilt development. H. galeatus had no effect on wilt. With Fusarium plus M. incognito or B. longicaudatus, high nematode levels promoted greater wilt than low levels. The combination of either population of B. longicaudatus with M. incognita and Fusarium induced greater wilt development than comparable inoculum densities of either nematode alone or where H. galeatus was substituted for either of these nematodes. Nematode reproduction was inversely related to wilt development. Without Fusarium, however, the high inoculum level resulted in greater reproduction of all nematode species on cotton. Combining M. incognita with B. longicaudatus or H. galeatus gave mutually depressive effects on final nematode populations. The interactions of H. gateatus with B. longicaudatus varied with two populations of the latter.     

The Influence of Phosphate Uptake on Cation Uptake in Fusarium oxysporum f. sp. vasinfectum

Fusarium oxysporum grown in a low phosphate medium was found to take up several times as much K from KH₂PO₄ as from KCI solutions. Large amounts of phosphate also were taken up from KH₂PO₄. Similar large uptakes of Na and phosphate took place from solutions of NaH₂PO₄. Substantial quanties of phosphate were taken up from solutions of Ca(H₂PO₄)₂ in the absence of any appreciable Ca uptake. When the fungus was grown in a medium containing high phosphate, little or no uptake of phosphate from KH₂PO₄ solutions occured and the K Uptake was at the same level as from KCI solutions. During large phosphate uptake sizable reductions in the organic acid content of the fungal cells were observed. Much, but not all, of the data could be explained on the basis of maintenance of charge balance within the cells. – The respiratory rate of fungus, grown in a low P medium, was markedly increased in KH₂PO₄ solution. Fungus, grown in a medium with high phosphate, had a higher respiratory rate which showed only a slight response to KH₂PO₄ solution. Fungus, grown in a medium with high phosphate, had a higher respiratory rate which showed only a slight response to KH₂PO₄.     

己二酸二异丁酯对辣椒种子萌发及枯萎菌的化感效应

采用模拟的方式,利用生物测定和室内培养的方法,研究了不同浓度的己二酸二异丁酯对辣椒种子萌发、幼苗生长及辣椒枯萎菌的化感效应.结果表明:己二酸二异丁酯对辣椒种子萌发和幼苗生长具有低浓度促进、高浓度抑制的化感效应;己二酸二异丁酯对辣椒和茄子种子的化感效应存在较大差异,在低浓度时对辣椒种子萌发和幼苗生长的促进作用强于茄子种子,而高浓度时对辣椒种子萌发和幼苗生长的抑制强度弱于茄子种子;各浓度己二酸二异丁酯对辣椒枯萎菌菌丝生长有极显著的抑制作用,且作用强度随着浓度增加而增强,当浓度为1 mnol·L~(-1)时抑制作用最强,抑制率为10.75%;在田间抗病性调查期间内各浓度处理均提高了辣椒幼苗的抗病性,其中以1 mmol·L~(-1)处理抗病性最好,病情指数比对照降低了49.88%.

Abstract：

By the methods of laboratory incubation and bioassay, a simulation test was conducted to study the allelopathic effects of different concentration diisobutyl adipate on pepper seed germi-nation and its seedling growth and Fusarium oxysporum f. sp. vasinfectum. For the pepper seed germination and seedling growth, diisobutyl adipate exhibited allelopathic promotion at low con-centration, but allelopathic inhibition at high concentration. There existed greater differences in the allelopathic effects of diisobutyl adipate on the seed germination and seedling growth of pepper and eggplant. The promotion effects of low concentration diisobutyl adipate on pepper were stron-ger than those on eggplant, while the inhibition effects of high concentration diisobutyl adipate on pepper were weaker than those on eggplant. All test concentration diisobutyl adipate had signifi-cant inhibition effects on the mycelium growth of Fusarium oxysporum f. sp. vasinfectum, and the effects increased with increasing diisobutyl adipate concentration, being the strongest (an inhibi-tory rate of 10. 75%) at 1 mnol·L~(-1). Field text indicated that diisobutyl adipate at all test con-centrations enhanced the disease resistance of pepper seedlings. The best effect was observed at 1 mmol·L~(-1) of diisobutyl adipate, with the disease index decreased by 49.88%, compared to the control.     

Fusaric acid and other metabolite production in Fusarium oxysporum f. sp. vasinfectum

A thin layer chromatography system is described for the analysis of fusaric acid and other secondary metabolites, to assist in the identification of pathogenic races of Fusarium oxysporum f. sp. vasinfectum . There were differences in the metabolite profiles of the races grown on different media.     

Differential interactions among cotton genotypes and isolates of Fusarium oxysporum f. sp. vasinfectum

Abstract

The pathogenicity of nine isolates of Fusarium oxysporum f. sp. vasinfectum (Fov) was evaluated on seedlings of 30 cotton (Gossypium barbadense L.) genotypes in 2005 and 2006. Isolate×genotype interaction was a highly significant (P < 0.01) source of variation in wilt incidence, suggesting that physiologic specialization exists within Fov isolates. Cluster analysis of aggressiveness of isolates and susceptibility of genotypes by the unweighted pair-group method based on arithmetic means (UPGMA) placed the isolates and the genotypes in several groups. Isolates were separated into two distinct groups. One group was closely related to race 5 while the other group was closely related to race 1. Cluster analysis also demonstrated that the Egyptian commercial cultivars had unique susceptibility patterns to Fov isolates remotely related to those of the other genotypes. The interaction between experiments of 2005 and 2006 was mainly due to a differential effect of years on the disease incidence for cotton cultivars.