Study of interaction between plant nutrition (N,P,K and Ca) and verticillios wilt disease (Verticillium dahliae) in cucumber.

Cucumber wilt disease caused by verticillium dahliae is one of the most important diseases of cucumber. Disease severity can to be decreased by plant nutrition management, especially nitrogen, phosphorus, potassium and calcium levels. For this purpose, interaction between plant nutrition and cucumber verticillios disease in cucumber was studied. Different levels of N, P, K and Ca on one current cultivar of cucumber were investigated at the presence and absence of fungus, using a factorial analysis based on completely randomized design with three replications. Significant different were observed among the different levels of elements used in this study. Presence of N, P, K and Ca increased the percentage of alive plants in comparison with control (distilled water + fungus). The effects of different levels of N, P, K and Ca were also investigated on growth of V. dahliae in vitro at a complete randomized design with three replications. Variance analysis of growth area of the fungus showed significant difference among some levels of the elements. The highest area growth of fungus was occurred at 0.1 gr/l of KNO3 and was 47/26 Cm2. The factors investigated, clearly suggested the occurrence of a wide interaction between cucumber nutrition (N, P, K and Ca) and V.dahliae and showed the importance of plant nutrituin management for decrease of disease severity.

A QTL analysis of sunflower partial resistance to downy mildew ( Plasmopara halstedii) and black stem ( Phoma macdonaldii) by the use of recombinant inbred lines (RILs).

Partial resistance to downy mildew ( Plasmopara halstedii) and to black stem (Phoma macdonaldii) in sunflower were investigated under natural field infection and a controlled growth chamber respectively. Genetic control for resistance to the diseases was determined in recombinant inbred lines (RILs) and their two parents, 'PAC-2' and 'RHA-266.' The experiments were undertaken in a randomized complete block design with two replications, in a field severely infected by downy mildew and in a controlled growth chamber with plants inoculated with an agressive French isolate of P. macdonaldii. Each replication consisted of three rows, 4.6-m long, giving 48 plants per RIL or parent in the field and 15 plants in the growth chamber. Genetic variability was observed among the RILs for resistance to both diseases. When 10% of the selected RILs were compared with the mean of the two parents genetic gain was significant for partial resistance to the diseases. Four putative QTLs for resistance to downy mildew on linkage groups 1, 9 and 17 were detected using composite interval mapping. The QTLs explained 54.9% of the total phenotypic variance. Major QTLs ( dmr1-1 and dmr1-2) for resistance were found on linkage group 1 with up to 31% of the phenotypic variability explained by two peaks. QTL analysis of resistance to black stem showed seven QTLs on linkage groups 3, 6, 8, 9, 11, 15 and 17. The detected QTLs together explain 92% of the phenotypic variation of the trait. Crosses between RILs contrasted for their resistance to downy mildew and black stem, and exhibiting molecular polymorphism in detected QTLs, will be made in order to focus more-precisely on the genomic region of interest.

Ultrastructural Studies of the Mode of Penetration by Phoma macdonaldii in Sunflower Seedlings.

ABSTRACT An ultrastructural investigation of the artificial inoculation of sunflower with Phoma macdonaldii conidia was undertaken using light, scanning, and transmission electron microscopy to elucidate the host-parasite relationship. The behavior of the conidia deposited on the cotyledon petiole was investigated at various time intervals after inoculation. Conidia adhesion and germination were observed first. The cotyledon petiole was invaded by the fungus directly through the cuticle and via stomata. Externally, the spore and germ tube were covered with a mucilaginous polysaccharide sheath of a cotton-like appearance and of variable thickness. At the time of penetration, the host cuticle was perforated mechanically. The cuticle was slightly depressed and no enzymatic alteration could be observed. The fungus did not form appressoria on the surface of the host tissues but developed an infection peg. As soon as the cuticle barrier was crossed, the fungus rapidly colonized the host parietal layer. In a first step, the plasmalemma of the host cell appeared to be stuck against the cell wall. As soon as the fungus passed through the epidermal cell wall to reach the host cytoplasm, the plasmalemma was disrupted, and the subsequent rapid breakdown of cell integrity favored the colonization of the tissues by the pathogen.