Reaction of melon (Cucumis melo L.) cultivars to soil-borne plant pathogenic fungi in Iran

The fungi Macrophomina phaseolina (Tassi), Monosporascus cannonballus (Pollack and Uecker) and Rhizoctonia solani (Kuhn) are responsible for significant destruction and melon crop losses in the Sistan region of Iran. In this study, eighteen melon cultivars were screened for resistance to these pathogens under greenhouse conditions twice. The melon cultivars were grown in pots and inoculated with each pathogen individually in three different experiments. None of the tested melon cultivars was immune to all the soil-borne plant pathogenic fungi. However, two cultivars, namely ‘Sfidak khatdar’ and ‘Sfidak bekhat’ were moderately resistant to all the three fungi. These melon cultivars are promising sources of resistance to M. phaseolina, M. cannonballus and R. solani, and should be the preferred choice for melon grown in infested areas. This study is the first report on screening of melon cultivars in Iran for resistance to M. phaseolina, M. cannonballus and R. solani and it reports the resistance of melon cultivars to three important soil-borne plant pathogens found worldwide.Key words: Melon, fungal resistance, Macrophomina phaseolina, Monosporascus cannonballus, Rhizoctonia solani

Physiological and genetic basis of 'Phytophthora' disease resistance in Sturt's desert pea, 'Swainsona formosa' (G.Don) J. Thompson (Fabaceae)

The susceptibility of Sturt's desert pea ('Swainsona formosa'), an ornamental legume with red, pink and white flowers, to fungal root pathogens such as 'Phytophthora cinnamomi', acts as a constraint to large-scale commercial production. Developing lines resistant to such pathogens is the most desirable method of control, as chemical control often results in chemical resistance or tolerance, and environmental pollution. Observations from the 'S. formosa' breeding program at the University of New England suggested that the white and pink lines may be more susceptible to root disease than the more common red line. Therefore, the objectives of this project were to establish whether a link exists between flower colour and resistance to 'P. cinnamomi', to identify any biochemical or physiological mechanisms of resistance to 'P. cinnamomi', and to determine whether it is possible to breed white or pink-flowered lines resistant to some common soilborne diseases

Flower colour is associated with susceptibility to disease in the legume 'Swainsona formosa'

The hypothesis that plants of the ornamental Australian native legume 'Swainsona formosa' (Sturt's desert pea) with reduced flower pigmentation are more susceptible to soilborne diseases was investigated using red, pink and white-flowered lines challenged with 'Phytophthora cinnamomi'. Inoculations of roots, hypocotyls and detached stems showed that the red line was completely resistant, the white line highly susceptible, and the pink line intermediate in reaction. Similar results were obtained for root and detached stem assays using 'Pythium' irregulare and 'Fusarium solani' isolated from diseased white-flowered plants, but all lines were equally susceptible to Botrytis 'cinerea' in detached stem assays. Crosses between the red and white lines showed that white flowers and susceptibility to 'P. cinnamomi' were each determined by recessive alleles at single loci, which segregated together

Jasmonic Acid Induced Systemic Resistance in Infected Cucumber by Pythium aphanidermatum

Damping-off disease of cucumber is one of the most destructive diseases of cucumber in worldwide. In this work, the potential of jasmonic acid (JA) for induce resistant against damping off disease was investigated. The effect of JA on activity of Polyphenol oxidase (PPO), Peroxidase (PO) and Catalase (CAT) enzymes and total phenol was assayed by spectrophotometric method. Expression level of three plant defense genes as Lipoxygenase, Cupi4 and Phenylalanine ammonia-lyase genes was analyzed using qRT-PCR method. Drop-plate method was used to assay inhibitory effect of JA on radial growth of fungi. Exogenic application of JA decreased disease severity in the infected plants but did not inhibit mycelia growth on solid medium compared to control. Our results showed that JA application substantially increased the activity of oxidative enzymes at different concentration. The highest enzyme activity was recorded after 48 hours post infection (hpi) at a concentration of 400 mg L-1 of JA. Gene expression analysis revealed that JA is differentially able to increase the mRNA transcripts of all tested genes at 48 hpi. The expression level of Cupi4 gene was higher than the other genes in treated plants. Induced systemic resistance by JA was mediated through an enhanced expression of ISR marker genes and increase of antioxidant enzymes activity. Based on these results, we suggest that exogenic application of JA could be considered as plant resistance inducer.&nbsp