نشریه تحقیقات بیماری های گیاهی
سال دوم شماره 2 (زمستان 1392)

The root and crown rot is one of the most important diseases of cucurbits in the world including Iran. In order to identify the causal agents of wilting and root and crown rot of cucurbits (watermelon، musk melon and cantaloupe) in Shahrood، investigations and collection of diseased samples were made in various fields of Shahrood، Mayamai and Biargomand regions during 2009-2010. After disinfection with sodium hypochlorite (1%)، pieces of infected tissues were cultured on potato dextrose agar (PDA) medium and /or pieces of infected tissues were cultured on PDA، CMA-PARPH and CMA-PARP media without disinfection. Isolates producing spores were purified with single spore method while isolates which did not produce spores، were purified using hyphal tip method. For pathogenicity tests، seedlings grown in green house were dipped in fungal spore suspension (106/ ml) by root dip method for spore producing fungi while in the case of isolates that did not produce spores، pathogenicity test was performed by placing small pieces of young culture of inoculum around crown and roots of plants being tested. According to the morphological، macroscopic and microscopic characteristics adapted from standard keys، pathogenic isolates were identified as Fusarium solani، F. oxysporum f. sp. melonis، F. oxysporum f. sp. niveum، F. equiseti، Phytophthora nicotianae and Rhizoctonia solani. F. oxysporum was the dominant isolated fungus. The results also showed that F. solani and F. oxysporum could be isolated during all growth stages of plants (seedling up to fruiting stages) and these species were widely spread throughout the region. All of these fungi are reported for the first time from melon fields of Shahrood.

The pink root rot disease، Phoma terrestris (syn. Pyrenochaeta terrestris) causes considerable losses in onion production of Isfahan، Iran. In this study، the effect of a suitable crop rotation system on 441 onion fields in the two main onion growing areas، Baraan and Ghahderijan for the two dominant cultivars، Texas-Early-Grano and Yellow-Sweet-Spanish was evaluated during 2009-1010. The results indicated that، in the fields where onions were grown in rotation with cereals، the disease severity and infection percentage were the least in comparison with other rotation types. Also، the orchards that were recently converted into field crops showed only 2. 83 percent disease severity. Infection rate of onion in rotation with vegetables، alfalfa، and when onion was planted more than one time in the last four years was 17. 66، 27. 00 and 36. 16%، respectively. Between the cultivated varieties، Texas-Early-Grano showed less infection and disease severity (20. 5%) compared with Yellow-Sweet-Spanish (24. 78%).

In this study، the ability of nematode-trapping fungus Arthrobotrys oligospora and salicylic acid (SA) were examined to control root-knot nematode، Meloidogyne javanica، in the laboratory and greenhouse conditions. Also changes of polyphenol oxidase (PPO) and peroxidase (POX) enzymes and total phenolic compounds accumulation in different treatments were studied. In greenhouse studies، we used leaf spraying of SA (5 mM) and soil drenching of A. oligospora (106 spore/ml) at six-leaf stage of the plants، separately and in combination. After 50 days of inoculation، diameter of the galls، number of galls and number of egg masses per individual plant، number of eggs per individual egg mass، root and foliage fresh weights were recorded. The data were analyzed in completely randomized design and subjected to analysis of Duncan’s multiple range test (p≤0. 05). The results showed that combined application of A. oligospora and SA were more effective compared to individual application of them. Study of changes in PPO، POX enzymes activities and total phenolic compounds accumulation showed that treatment with these factors caused increase in enzyme activities and also accumulation of total phenolics which shows induction of plant defense system.

In this study، the effect of salicylic acid (SA) on response of wheat cultivars (2 susceptible and 2 resistant cvs.) to Septoria was evaluated. The SA was used in two methods; it was sprayed on the wheat leaves and/or the seeds were drenched in SA solution. Two isolate of Mycosphaerella graminicola S1 and K8 were used in this study. The pathogenicity of isolate S1 was more than K8; therefore this isolate was selected for further experiments. In the test of evaluation disease interaction with SA، Zagrus cultivar showed the least disease severity (41%) at 4 mM SA level، and Atrak cultivar was showed the most disease severity in 0. 5 mM SA level، 81%. Four densities of SA were used for seed treatment (0، 0. 5، 1 and 2mM)، the maximum controlling of disease was achieved at 1mM level of SA. The results of this study suggest the best concentration for spraying on wheat leaves is 2 mM of SA، and 1 mM is the best concentration for seed treatment.

The biocontrol agents Candida membranifuciens (A5)، Pichia guilliermondi (A6) alone and in combination with silicon (Si) were tested for biological control of the gray mold of apple caused by Botrytis cinerea. Results showed that Si decreased the growth of the yeast isolates A5 and A6 in vitro. Also silicon inhibited the growth of the pathogen at concentration above 0/8% w/v Results of storage experiments indicated that، the lesion diameters in treated fruit with the biocontrol combinations of Si % 0/2 +A5andSi % 0/2+A6 were 3/87 and3/48 mm respectively، at 4 C° and for Si % 0/2 +A5 was 5/23 mm at 20 oC، showing better control than the other treatments. The combination of Si %0/2 +A5 caused a decrease in catalase activity 4 days after inoculation with pathogen. This combination increased peroxidase activity and Phenolic accumulation that reached maximum level 2 days after pathogen inoculation. These results indicate that using antagonists in combination with silicon may result in further induction of resistance in apple fruits and improve biological control.