Races Of Fusarium Oxysporum Research Articles

Determinação das raças fisiológicas do Fusarium do tomateiro de Pernambuco

Os autôres, utilizaram as variedades de tomates Santa Cruz e S-34 como variedade sdiferericiais, para determinar raças fisiológicas de Fusarium oxysporum f. lycopersici (Wr) Sny & Hans. Testaram 7 isolamentos do patógeno, retirados de material proveniente de Pernambuco, em condições de casa de vegetação com contrôle parcial de temperatura e concluiram que todos os 7 isolamentos reagiram como sendo da raça 1, e que houve variação na patogenicidade entre eles.

Some effects of pea root exudates on physiologic races of Fusarium Oxysporum Fr. F. pisi (Linf.) Snyder & Hansen

Exudates from the roots of the pea cultivars, Onward, Alaska and Delwiche Commando, which differentiate between three physiologic races of Fusarium oxysporum f. pisi , affected spore germination in the three races differentially, depressing the germination of races they resisted more than of those to which they were susceptible. Exudates from young seedlings depressed germination more than did those from roots of older plants, and the activity of exudates increased temporarily when side roots were first formed. When concentrated root exudates were contained in porcelain cylinders on agar sown with spores, zones of differential growth formed around the cylinders; when the exudate was from a cultivar resistant to the race whose spores were plated, the zone was one of growth inhibition, and when from a susceptible cultivar, it was one of growth stimulation. Notwithstanding this effect on spore germination, exudates from the different cultivars had no differential effect on the rate at which germ tubes or mycelium of the individual races grew. Sections through roots of cultivars inoculated with a race they resist showed that the mycelium invaded only the outer cortex. Plants susceptible to F. oxysporum wilt less when simultaneously infected with F. solani ; xtracts of the bases of pea plants infected with F. solani inhibited the germination of spores of F. oxysporum , whereas extracts from normal stem bases did not.

Differential rhizosphere effects of three pea cultivars on physiologic races of Fusarium oxysporum f. pisi

Pea cultivars Onward, Alaska and Delwiche Commando, differential hosts for three physiologic races of Fusarium oxysporum f. pisi (cause of pea wilt), exert different effects on the soil microflora. Cultivar Onward, susceptible to race I, supports more fungi, bacteria and Actinomycetes near its root surface than do either Alaska or Delwiche Commando, which resist race I. Qualitative differences between rhizosphere populations of the three cultivars are most apparent in Fusaria and bacteria. The germination of spores of the three physiologic races of F. oxysporum f. pisi was affected by water extracts of the three rhizosphere soils in the same way as earlier with root exudates from the three cultivars. Spores of a race able to wilt a particular cultivar germinate well in rhizosphere soil extract from that cultivar. Germination is decreased, on the other hand, in extracts from the rhizosphere of a resistant cultivar. Spores of race 3, however, were not able to germinate well in rhizosphere extract of cultivar Alaska, which is susceptible to this race. Soils in which each of the three pea cultivars had grown were inoculated with spores of race I and planted with seedlings of the susceptible cultivar Onward. Plants became severely wilted in pots in which Onward had grown and in control pots which had not grown peas, but wilting was less and developed more slowly in pots which had previously been cropped with cultivars Alaska and Delwiche Commando (which resist race I). It is suggested that substances exuded by roots of cultivars resistant to race I, together with the effect of altering the soil microflora, prevent race I from germinating, thus lowering the amount of effective inoculum and delaying the onset of wilt.