A. Aly

Frequency and diversity of Fusarium spp. colonizing roots of Egyptian cottons

Abstract Fusarium species are known to play a role in several diseases of cotton including the seedling disease complex, wilt, and boll rot. Therefore, a mycoflora study was conducted in 1998 in order to identify Fusarium species found in association with cotton roots. A total of 109 samples of cotton seedlings infected with post-emergence damping-off or rotted roots of adult plants were obtained from different cotton-growing areas in Egypt. Forty-six isolates were recovered and were identified as follows: F. oxysporum (28 isolates), F. moniliforme (9), F. solani (6), F. avenaceum (2), F. chlamydosporum (1). F. oxysporum, F. moniliforme and F. solani, the dominant species, accounted for 60.9%, 19.6% and 13% of the total isolates, respectively in 1998. F. oxysporum showed the highest isolation frequency in Beharia and Minufiya while F. moniliforme showed the most isolation frequency in Minufiya and Gharbiya. F. oxysporum was one of the major taxa of the Fusarium assemblage from Giza 70. F. oxysporum showed the most frequently isolated fungus in May while F. moniliforme and F. solani were the most frequently isolated fungi in August. Isolation frequency of Fusarium spp. during July and August was significantly greater than that of April or June. This implies that cotton roots are subjected more to colonization by Fusarium spp. as plants mature. Regarding pathogenicity, of the 46 isolates of Fusarium spp. tested under greenhouse conditions, 38 isolates (82.4%) were pathogenic to seedlings of Giza 89. This study indicates that F. oxysporum and F. moniliforme are important pathogens in the etiology of cotton damping-off in Egypt.

Examination of Correlations Between Several Biochemical Components and Powdery Mildew Resistance of Flax Cultivars

A field trial was conducted in 2009/2010 and 2010/2011 growing seasons at Giza Agricultural Research Station to examine correlations between some biochemical componets and powdery mildews (PMs) resistance in flax cultivars. Nine flax cultivars could be divided into five distinct groups, i.e., highly susceptible (Cortland and C.I. 2008), moderately susceptible (Giza 7, and Marshall), moderately resistant (Cass), resistant (Koto, Dakota and Wilden), and highly resistant (Ottowa 770B). The cultivars showed considerable variation in PM severity ranged from 8.05 on Ottowa 770B to 97.02% on Cortland. Total soluble proteins, total phenols, antioxidant enzymes (peroxidase and polyphenoloxidase), ascorbic acid, tocopherol, and malondialdehyde (MDA), were determined in uninfected leaves of the tested cultivars. Pearson’s correlation coefficient was calculated to measure the degree of association between PM severity and each component. All components showed significant (P < 0.05) or highly significant (P < 0.01) negative correlation with PM severity except MDA, which showed positive correlation (P < 0.01). Linear regression analysis was used to evaluate the causal relationship between the biochemical components (independent variables) and PM severity (dependent variable). Coefficient of determination (R 2 ) values of the generated models ranged from 48.76 to 77.15%. Tocopherol, MDA, and proteins were the most important contributors to the total variation in PM severity as the R 2 values of their models were 71.78, 75.28, and 77.15%, respectively. The results of the present study suggest that tocopherol, MDA, and proteins in uninfected leaves can be used as biochemical markers to predict PM resistance in flax.

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.

Response of Commercial Cotton Cultivars to Fusarium solani

Twenty-nine isolates of Fusarium solani, originally isolated from diseased cotton roots in Egypt, were evaluated for their ability to cause symptoms on four genetically diverse cotton cultivars. Analysis of variance showed highly significant variance among cultivars, and isolates as well as the isolate x genotype interactions were highly significant(p

Effect of fatty acid content on the level of cottonseed colonization by fungi

Effect of fatty acid content on the level of cottonseed colonization by fungi Non-sterilized seeds of 12 Egyptain cotton (Gossypium barbadense L.) genotypes were examined for qualitative and quantitative estimates of seed-borne fungi. Rhizopus stolonifer (39.7%), Aspergillus niger (33.5%), and Penicillium sp. (23.3%) were the most predominant fungi isolated from the seeds. Other fungi occurred at frequencies that ranged from 0.3 to 17.7%. Gas-liquid chromatography (GLC) analysis of fatty acid composition of the seeds revealed the presence of the following fatty acids: caproic, caprylic, capric, lauric, myristic, palmitic, margaric, stearic, oleic, linoleic, and linolenic. The total mean percentage of the monounsaturated fatty acids was 59.11%, while that of the unsaturated fatty acids was 16.72%. Isolation frequencies of Alternaria alternata, A. flavus, A. niger were not significantly correlated with the content of any fatty acid. Isolation frequencies of the other fungi were significantly correlated with the content of 1-2 fatty acids. Cladosporium sp. was a notable exception because its isolation frequency was significantly correlated with the content of caproic (r = 0.926, p < 0.01), caprylic (r = 0.638, p < 0.05), palmitic (r = -0.586, p < 0.05), and linoleic acid (r = 0.917, p < 0.01). It was possible to group the isolated fungi into 5 distinct categories based on their sensitivity to the fatty acids (the magnitude of R2 values). The results of the present investigation suggest that certain fatty acids regulate the colonization of cottonseed by fungi, and that the control of these fungi may be possible by modifying the fatty acid content of the seed.