نشریه کنترل بیولوژیک آفات و بیماری های گیاهی
سال یازدهم شماره 2 (پاییز و زمستان 1401)

Entomopathogenic nematodes are valuable biocontrol agents of pests. The use of indigenous isolates compared to imported isolates has advantages including compatibility with the environment and native pests and not causing adverse effects on indigenous species. In the present study, the effect of native isolates of Steinernema carpocapsae and Steinernema feltiae on model host, Tenebrio molitor was compared with exotic commercial products by two bioassay methods (in Petri dishes and soil). Probit analysis showed a significant correlation between the nematode concentrations and the insect mortality (R2 ≥ 0.90). The Iranian S. carpocapsae isolate showed the lowest LC50 value (5 IJ Larva-1) and the commercial S. feltiae isolate showed the highest LC50 value (7 IJ Larva-1). However, based on the LC50 ratio values there was no significant difference between the four nematode isolates. The comparison of the mortality percentage of the pest in soil bioassay showed a similar effect of native isolates with commercial isolates (P ≤ 0.01). The impact of native nematode isolates on par with commercial isolates which had been selected among numerous isolates, showed their high potential Therefor, basic research with the aim of developing the practical application of these valuable agents is suggested.

Modern agriculture in the 21st century must provide food security for this growing population, which means producing more food and fiber with less labor. Therefore, agriculture in this century requires smart investment based on more efficient and environmentally friendly production methods. Common wheat root rot caused by B. sorokiniana is one of the most important pathogens of wheat, which causes economic losses every year. In this research, from 180 Bacillus isolates from the samples collected from the wheat fields of Hamadan province, wastes of edible mushrooms, palm wastes and wood wastes, 9 isolates were able to produce γ-PGA with different production rates. 2 isolates were able to produce γ-PGA independently of glutamic acid. Bacillus velezensis UTB97 with a production rate of 40 g/L γ-PGA was selected as the superior producer isolate. UTB97 could prevent 65% growth of pathogenic fungi in laboratory conditions by dual culture method. Greenhouse result showed that the treatment of UTB97 and UTB97 + γ-PGA was able to control Common wheat root rot disease by 59 and 73%, respectively, compared to the control treatment, and also the treatment of UTB97 + γ-PGA was able to increase the growth index of wheat. (stem length and root dry weight), in the presence and absence of the pathogenic fungus.

One of the important aspects of the field application of entomopathogenic nematodes is their compatibility with common chemicals in agricultural systems. In this research, the effect of bio-rational insecticide, flubendiamide on the survival and pathogenicity of native entomopathogenic nematode isolates, Steinernema carpocapsae IRMoghan1 and Steinernema feltiae was evaluated. For the survival experiment, nematode suspensions (500 IJml-1) were prepared in 150 ml recommended dose of flubendiamide (25 ppm) and at different time intervals (24, 48 and 72 hours and seven days) survival percentages of the nematodes were recorded. For the pathogenicity experiment, the nematodes that were exposed to the insecticide were used in the bioassay against Galleria mellonella (concentration of 150 IJ Larvae-1) and the mortality of the insects was recorded after 72 hours. Based on the results of variance analysis, S. carpocapsae IRMoghan1 showed higher mortality compared to S. feltiae due to flubendiamide treatment (P ≤ 0.01). Also, after 24 hours and 48 hours of treatment with flubendiamide, the lowest percentage of mortality and seven days after the treatment, the highest mortality rate of the nematodes were observed (P ≤ 0.01). Statistical analysis of the bioassay results of nematodes recovered from different time treatments with flubendiamide insecticide on G. mellonella larvae showed no significant difference between two nematode isolates (p˃0.05). Flubendiamide was considered compatible with and harmless (Class 1) to both native isolates according to IOBC/WPRS. Compatibility of the native isolates is a valuable characteristic for application development of EPNs in the country.

Seed coating using antagonistic fungi protects seeds and plants against pathogens. In this research, the effect of tomato seed coating was studied using the endophytic fungus Acrophialophora jodhpurensis against Rhizoctonia solani in vivo. Seed coating was done using the spores of A. jodhpurensis supplemented with 1% edible sucrose, 0.5 % carboxymethyl cellulose (CMC), or 0.5 % molasses as stickers. The greenhouse studies showed that the plant roots were colonized by this endophytic fungus very well at 30 days post-cultivation. The colonization of the roots in sucrose and carboxymethyl cellulose treatments was 80.55%, and in molasses treatment was 69.44%. This beneficial fungus significantly reduced the disease index of R. solani on detached leaf discs and tomato seedlings compared to the control. Also, the formation of pathogen infection structures, such as lobate appressoria and infection cushions, reduced on the treated plants compared to the control. Plant growth parameters such as dry and wet weight, shoot and root length significantly increased when the tomato seeds were coated with A. jodhpurensis compared to the non-treated control. Among the different coating materials used as sticker, sucrose was found to be the most effective for reducing the disease severity of R. solani and increasing plant growth parameters, which in sucrose, A. jodhpurensis and R. solani treatment the disease index significantly reduced compared to the plants only inoculated with R. solani. Therefore, seed coating using the endophytic fungus A. jodhpurensis supplemented with stickers, particularly edible sucrose, can be applied to protect tomato plants against this destructive pathogen..

Unrestricted use of chemical insecticides, especially at high concentrations, has reduced their efficacy. Plant-based pesticides, due to their relatively high safety levels to humans and environment as well as effective control on insects, have become a suitable alternative to conventional pesticides. The aim of this study was to investigate the biological and physiological effects of the formulated essential oil of Trachyspermum ammi (L.) on the larvae of Helicoverpa armigera Hüb. The obtained essential oil was formulated into an emulsion using Tween 20 as emulsifier. Chemical analysis of the extracted essential oil indicated that Terpinen (14.4%), Cymene (18.5%), and Thymol (61.6%) were the major compounds. The essential oil of T. ammi have a significant repellency rate on third and sixth instar larvae of cotton bollworm at different observed time intervals, with an average repellency rate of 61-76%. Regarding fumigant toxicity, the highest concentration of the essential oil (500 µL/L) resulted in 100% larval mortality. The LC50 value for fumigant toxicity measured as 82.73 µL/L. The duration of larval development significantly increased in treatments compared to control. In EO concentrations of 2.5-1.25 percent an increase was observed respectively in the duration of the larval stage by 9 and 7 days. The pupae and adult’s emergence affected in dose dependent manner. At concentration of 50 µl/l, 89% inhibition of protease enzyme recorded. With regards to the biological and physiological effects observed in the formulated T. ammi essential oil, with complimentary researches, it could be used in integrated management programs of cotton bollworm.

The entomopathogenic bacterium,Bacillus thuringiensis, is a gram-positive and spore-forming bacterium, and a large number of its subspecies have been identified and introduced. The insect immune responses activate after ingesting Bt or its toxin proteins. This research aimed to investigate the effect of temperature and three subspecies including B. thuringiensis subspecies thuringiensis (Btt), B. thuringiensis subspecies aizawai (Bta), and B. thuringiensis subspecies galleriae (Btg) on nodule formation and some biological parameters of the moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). A concentration of 109 spore/ml was used to contaminate the larval diet. This experiment was performed at three different temperatures (20, 25, and 30 ºC), relative humidity of 55±5%, and a photoperiod of 16:8 (L: D). The highest number of nodules was significantly observed in Bta and Btg treatments at 30 ºC and the lowest number of nodules was observed in the control. There was no significant difference in the time until pupation at any temperature among the three subspecies. However, a significant difference was observed between different temperatures in each subspecies. Therefore, this duration in the control was significantly affected by temperature. The highest amount of pupa production was related to the temperatures of 20 and 25 ºC in subspecies Bta and the control that had no significant difference. The number of adults obtained in the Bta treatment was not affected by the temperature, similar to the control. Since the temperature did not affect the number of nodules in the control, it is concluded that increasing the temperature by affecting the Bt increased the number of the nodules formed in the surviving larvae and also, the subspecies kind of the bacterium had a significant effect on it.