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Characterization, Inheritance, and Mechanism of Resistance to Fusarium solani in Passionfruit (Passiflora edulis Sims.)
Abstract:
Eight accessions of passionfruit were crossed to produce an F1 generation. This was accomplished by crossing all possible combinations with reciprocal and sib-mating resulting in 64 crosses. In addition, sibmating of F1 progenies were also done. Seven Fusarium isolates were collected in Rayong province and Khon Kaen University, both in Thailand. Out of these, four Fusarium species were identified, namely: 1) F. oxysporum, 2) F. solani, 3) F. .fusariodes, and 4) F. semitectum. One isolate of F. solani collected from Rayong province (FPR) showed a high degree of pathogenicity on passionfruit. Segregation of progenies from F1 lines showed no definite patterns to ascertain the number of genes controlling resistance to F. solani. However, it was found that incubation period plays a major role in the expression of resistance to F. solani. Furthermore, it can be deduced that resistance was controlled by multiple genes and maternal influence. The latter was exemplified by P. edulis (PNG) when used as female parent. Generally, higher heritability estimates were obtained in all accessions when used as female.
Resistant plants, both infected and uninfected with F. solani, exhibited different morphology on its stem base compared to that of uninfected susceptible plant. A thick-walled cell appeared between the cortex and the vascular cambium, which formed into continuous cylinder cells. This was the result of the gelation formation in vascular fiber cells, which acts as a pre-existing morphological mechanism to prevent the mycelium of F. solani from invading and gaining access to the vascular system.
Results obtained from the extraction and separation of phenolic compounds using thin-layer and gas-liquid chromatography, and cyanogenic glycosides by thin-layer chromatography showed that there was no difference and biochemical units within resistant lines, both infected and uninfected, and uninfected susceptible lines with F. solani. This indicated that phenolic compounds and cyanogenic glycosides do not play a major role in the biochemical mechanism for resistance to F.solani in passionfruit.