فصلنامه گیاه پزشکی
سال چهل و ششم شماره 3 (پاییز 1402)

Rice stem borer, Chilo suppressalis Walker (Lep.: Crambidae), is one of the most important and destructive rice pests in the world, including Iran, especially in the northern provinces. Every year, a significant amount of chemical insecticides are introduced into the environment to control this pest, which has caused many concerns in human health (rice farmers and consumers) and other organisms (aquatic, birds, livestock, etc.). Therefore, replacing high-risk chemical insecticides with environmentally friendly and safe compounds can reduce the side effects of pesticides and reduce the occurrence of resistance in this pest to the insecticides used and, as a result, control it more effectively. This study was conducted to compare the effectiveness of several common biological and chemical insecticides to control the rice stem borer, C. suppressalis.For this purpose, a study was designed as a randomized complete block design with six treatments and four replications and was carried out in a field located in Hashemabad village, Gorgan city, Iran. The experimental treatments included chlorpyrifos (Dursban®, EC 40.8%, 2 L/hectare), fipronil (Regent®, SC 50%, 1 L/hectare), fenitrothion (Sumithion®, EC 50%, 1.5 L/hectare), B.T. (1 L/hectare), Matrin (Rui Agro®, SL 0.6%, 1 L/hectare), and a control group (water foliar spraying). Additionally, the larval population was sampled one day before foliar spraying and 3, 7, and 14 days after foliar spraying. The Henderson-Tilton formula was used to calculate the mortality rate (insecticide efficiency). Analysis of variance was performed using the GLM model with SAS software.Means were compared using Duncan's multi-range test at the 5% probability level.The analysis of variance indicated significant differences among the treatments in terms of stem infection percentage and death of the central bud at 7 and 14 days after treatment application. Additionally, the analysis of variance results for stem contamination after 14 days of insecticide application revealed that all insecticides could reduce stem contamination compared to the control treatment, with some insecticides falling within the same statistical group. Regarding the effectiveness of the treatments in controlling the rice stem borer, the analysis of variance results showed that chlorpyrifos, Matrine, and fipronil were the most effective insecticides, followed by fenitrothion and BT, at 3 days after treatment application. At 7 days after treatment application, chlorpyrifos exhibited the highest efficiency, averaging 81.24%, which was not significantly different from fipronil and Matrine. Fenitrothion and BT insecticides demonstrated the lowest efficiency. The same trend persisted 14 days after treatment application, with chlorpyrifos achieving the highest efficiency at an average of 85.85%. There were no significant differences between chlorpyrifos, fipronil, and Matrine, which had efficiencies of 79.65% and 78.97%, respectively. BT insecticide recorded the lowest efficiency level at 54.18%, which was significantly different from the other insecticides.Based on the present study's findings, it is evident that insecticides such as Chlorpyrifos and Fipronil, which have been extensively used in Iran for the chemical control of the rice stem borer, have raised concerns regarding the development of resistance in this pest. Therefore, it is advisable to consider alternatives such as Matrine, which is safer and less hazardous. Matrine, with its distinct mode of action, can serve as a highly suitable option for controlling the rice stem borer while reducing the likelihood of resistance development against insecticides.

Entomopathogenic fungi (EPF) are the key elements for pest management in sustainable agriculture. Many EPFs can produce secondary metabolites with toxic effects, which playing an essential role in their pathogenicity. In this study, the metabolites of some EPFs, including three isolates of Akanthomyces lecanii species (PAL6, PAL7, and PAL8) and one isolate of A. muscarius species (AGM5), were biochemically analyzed. Extracellular metabolites were isolated from the fungal cells of the two-week-old culture of each isolate, and the chemical constituents were identified using by high-performance liquid chromatography (HPLC). During the retention times interval of 10-13 minutes, four different peaks were observed within metabolites of the isolates PAL6, PAL7, and PAL8. In the case of the AGM5 isolate, ; however, one peak was observed at 11.53 retention time. Comparative analysis showed the presence of insecticidal toxic cyclic peptides such as bassianolide within the fungal metabolites. Moreover, one peak with a new identity was detected within the metabolites from the fungal isolates of PAL6, PAL7, and PAL8 in the retention time interval of 5 minutes, from the isolate AGM5 at 11.53 retention time. The results demonstrated that the production ofproducing toxic compounds such as bassianolide by the EPF probably contributed to their insecticidal effects.

Strip cultivation is one of the effective methods to reduce the population of pests and increase the abundance and diversity of natural enemies in any habitat. Onion thrips, Thrips tabaci Lind., is a pest of onion (Allium cepa L.) worldwide. Larvae and adults of thrips feed on cell sap and cause silver spots on the surface of leaves of onion plants that consequently result in a significant reduction in onion yield. Control of onion thrips is difficult due to the short generation time, high fecundity, and the emergence of insecticide-resistant genotypes. Predators in each region, such as hemipterans, ladybugs, syrphid flies, carabid beetles, mites, and spiders, are effective in the biological control of the onion thrips population in fields. Intercropping systems can affect the biological control of pests by providing food and habitat resources for natural enemies. Therefore, designing effective and appropriate methods to reduce the population of onion thrips and increase the diversity and abundance of natural enemies can effectively manage T. tabaci in fields.

In this study, the effect of intercropping four rows of onion (Allium cepa L.) with two rows of fenugreek (Trigonella foenum-graecum L.) (4O:2F) and four rows of onion with two rows of safflower (Carthamus tinctorius L.) (4O:4S) was investigated on densities of the onion thrips, biodiversity of predators, and crop yields in 2022 and 2023. The experiments were accomplished in a randomized complete block design with two intercrops of 4O:2F and 4O:4S along with the sole crops. The density of onion thrips and predators per plant was counted and recorded on weakly sampling dates by direct counting using a magnifying glass. The predatory species that we suspected in their identification were transferred to the laboratory and carefully identified through morphological characteristics under a stereomicroscope. The average annual abundance of each predator species and the abundance of predators per plant in each plot were calculated during the onion growing season. In addition, Shannon's diversity index (H') and Pielou's evenness index (J') were calculated for the complexity of predators in each plot and in each tested year to compare the cropping systems. The onion, fenugreek, and safflower yield per square meter were estimated in strip intercropping systems and single crops. Then, the land equality ratio (LER) was calculated for both intercrops to estimate the yield advantage regarding the monoculture of each crop.

Three intercrops led to a significant reduction in the densities of larvae and adults of onion thrips compared with sole onion. Further, the leaf damage index was lower in intercrops than in single onion in two seasons. A significant coefficient of determination (R2) was calculated between the leaf damage index and the dry weight of onion per plant in two intercrop and sole onions. The total abundance of predators was higher in intercrops, especially 4O:2F than in the sole crop. More values of the Shannon diversity index and the Pielou's evenness index for predators were recorded in intercrops compared with the sole crop in two seasons. The dry yield of onions per square meter was more significant in both strip intercropping systems compared to single onions in 2022 and 2023. On the contrary, the dry yield of fenugreek and safflower per square meter was insignificant among intercrops and single crops in two years. The highest land equivalent ratio (LER) was calculated for 4O:2F.

Overall, the intercropping of onion and fenugreek (4O:2F) and onion and safflower (4O:2S) demonstrated a reduction in the population of onion thrips. Both intercrops, particularly 4O:2F, contributed to an increase in the abundance and diversity of predators and the values of LER when compared with sole crops. As a result, farmers could consider implementing both intercrops, particularly 4O:2F, as an environmentally conscious approach to managing T. tabaci in the field.

Body size has a profound effect on many aspects of animals’ biology including sexual interactions. Hymenopteran parasitoids exhibit dimorphisms in which females are larger than males. A recent study has shown that in the solitary koinobiont parasitoid wasp Lysiphlebus fabarum Marshall, offspring life history traits are influenced by maternal body size which raises the questions of whether larger females are preferred and whether larger males have an advantage when it comes to accessing larger mates. To test this, females of L. fabarum were allowed to lay eggs in aphids (Aphis fabae Scopoli) at different growth stages to manipulate female and male body size. First, we conducted a choice experiment to determine whether large female wasps are preferred by males. Second, we examined the effect of male body size on the ability of males within a patch to access females. Males of L. fabarum lack mate preference, as both small and large females were almost equally selected as mates. Mate searching duration did not vary with male or female body size, suggesting body size does not influence pre-copulatory interactions within the patch. Smaller males copulated significantly longer, and copulation duration increased with the sexual body size dimorphism. Our finding suggests that a “first-to-mate” strategy is favoured by males, mating with the female they encounter regardless of her quality. Also, small males copulate longer possibly because of lower sperm transfer rate. This study shed light on the evolutionary processes regarding mating behaviours in this parasitoid wasp.

The escalating concerns regarding the adverse effects link to pesticide utilization against stored-product pests have amplified interest in exploring safer alternative approaches, notably physical methods. Temperature management, a prominent avenue within physical control, is considered one of the most promising strategies against these pests. This investigation scrutinizes the effectiveness of elevated temperatures on adult Trogoderma variabile, Callosobruchus maculatus, Lasioderma serricorne, Oryzaephilus surinamensis), and Plodia interpunctella.

Experiments employed one-day-old adults. High temperatures (40, 43, 46, 50 and 54 °C) were regulated using an electric oven (Memmert, Germany). Initially, each species underwent individual assessment in preliminary tests, establishing eight exposure durations for the main bioassays. Within each exposure duration, groups of one-day-old adults (4 replicates, comprising 25 male and 25 female adults per replicate) were housed in glass Petri dishes. Upon completion of the exposure period, adults were relocated to ambient room conditions (21-27 °C; 55-70% R.H.). Subsequently, deceased males and females were tallied after a 24-hour interval.

Both male and female adults across all species exhibited equivalent sensitivity to supra-optimal temperatures. As anticipated, higher temperatures significantly reduced the LTs; however, distinct response patterns were observed among the studied species. At 40 °C, the LT50s for T. variabile, C. maculatus, L. serricorne, O. surinamensis, and P. interpunctella were approximately 18, 9, 47, 34, and 7.5 h, respectively. At 54 °C, these times decreased to about 7, 4, 12, 8 and 8 min, respectively. Correspondingly, the LT95s at 40 °C these pests were approximately 3.7, 4.8, 5.7, 5.5, and 1.9 days, respectively, whereas at 54 °C, they reduced substantially to about 20, 18, 23, 14, and 26 min, respectively. For T. variabile, the LT50s at 43, 46, and 50 °C (approximately 13, 11.3, and 11 min, respectively) were roughly 1.7 times longer than that at 54 °C (around 7 min). Conversely, at 40 °C, the LT50 was considerably lengthier (1077 min). C. maculatus adults displayed LT50 values at 46 and 50 °C (around 8 and 9 min, respectively), roughly twice as long as those at 54 °C (4 min). At 40 and 43 °C, the LT50s were notably longer (543 and 67 min, respectively). In the case of L. serricorne, solely the LT50 at 50 °C was approximately twice as long as that at 54 °C (approximately 12 min). At 43 and 46 °C, however, the requisite LT50s were lengthier (about 167 and 80 min, respectively), while at 40 °C, the LT50 was substantially longer (about 2820 min). For O. surinamensis adults, the LT50s at 43, 46, and 50 °C were approximately 1.3 to 1.5 times longer (about 13, 12, and 11 minutes, respectively) than that at 54 °C (about 8 min, with the LT50 at 40 °C being notably longer (about 2048 min). Concerning P. interpunctella, the LT50s at 46 and 50 °C were roughly three (about 27 min) and two (about 18 min) times greater than the LT50 at 54 °C (about 8 min). At 40 and 43 °C, the LT50s were considerably longer (about 449 and 98 min, respectively). In general, based on both LT50 and LT95 L. serricorne emerged as the most tolerant species, while C. maculatus, according to LT50 and O. surinamensis based on LT95 appeared to be the most sensitive species to high temperatures.

Despite the varied responses observed among adult stored-products insects to supra-optimal temperatures, the comparison between estimated LT50s and LT95s indicated the notable efficacy of high temperatures, particularly at 50 and 54 °C, in inducing substantial mortality rates. This effectiveness ranged from approximately 23 min for L. serricorne to 14 min for O. surinamensis, resulting in 95% mortality. Our findings underscore the potential of high temperatures as a pivotal tool in the management and mitigation of economic losses caused by the five studied pests. The outcomes of this research advocate for the significant role that elevated temperatures can play in addressing these pests. Considering our results in conjunction with existing reports on the effects and efficiency of high temperatures, the physical control method utilizing elevated temperatures emerges as a viable alternative to chemical insecticides for controlling stored-products moths and beetles. This method holds promise and can be incorporated into pest management programs targeting these particular pests.

Chickpea, cultivated in rainfed and irrigated fields across many countries, faces biological stresses such as Ascochyta blight caused by the pathogenic fungus Ascochyta rabiei. This disease poses a severe threat to chickpea fields, resulting in substantial annual damage in various countries. Identifying resistance sources through molecular methods, specifically genomic tracking of the resistance trait, holds the potential to expedite and enhance control measures effectively. The use of the Amplification Refractory Mutation System (ARMS) method, involving functional point mutations and resistance-related alleles, proves highly efficient in advancing selection programs targeted at combating Ascochyta blight.

The fragment harboring the SNP18-Pos57723 point mutation within the GSh118 gene sequence underwent amplification and sequencing using PSh118-F/R specific primers. This process utilized DNA extracted from both resistant (MCC113) and susceptible (ILC263) chickpea genotypes. The identification of alleles associated with resistance and sensitivity was established. Distinct differentiating primers were formulated for resistant (PSh118-Fc and PSh118-R) and sensitive (PSh18-Fg and PSh18-R) genotypes. The specific annealing temperature for each reaction was determined through a temperature gradient analysis. The efficacy of the designed primers in distinguishing between resistant and sensitive genotypes was assessed by conducting PCR and comparing their electrophoresis patterns.

The presence of alleles linked to GSh18-2773C resistance and GSh18-2773g sensitivity was confirmed in resistant and sensitive chickpea genotypes, respectively. The specific primers PSh18-Fc and PSh18-R, designed for detecting the resistance allele, successfully amplified the expected 330 bp fragment in the resistant chickpea genotype MCC133. The study results affirmed the accurate amplification of alleles using these designated primers.

In the present study, the ARMS method, known for its high sensitivity, specificity, rapidity, cost-effectiveness, multiplexing capabilities, compatibility with high throughput methods, and non-destructive nature, was employed to differentiate chickpea genotypes resistant to Ascochyta blight. The ARMS method's effectiveness in selecting resistance sources among various plant lines and cultivars has been demonstrated through allele tracking related to the resistance gene in prior studies. The results of this study indicated that the ARMS method accurately distinguishes chickpea genotypes resistant and sensitive to Ascochyta blight based on alleles associated with the GSh18-2773 position's point mutation. Thus, employing specific primers for the resistance allele is recommended in molecular selection studies of chickpea sources resistant to Ascochyta blight.

Stem rust, or black rust, caused by the fungus Puccinia graminis f. sp. tritici, poses a severe threat to global food security, potentially devastating wheat crops on farms. The damage of this disease in the epidemic condition is 100% of the wheat crops. Frequent epidemics of stem rust have been reported in different regions of the world in the past years. The most effective method to control this disease is identifying and incorporating effective resistance genes from resistant cultivars into desirable wheat genotypes, for establishing durable genetic resistance.

To identify new sources of resistance, an experiment was conducted to investigate the resistance reactions of 30 wheat genotypes and a susceptible check (Morocco) against six Pgt races with distinct pathogenicity patterns (TKTTF, TTTF, TTRTF, PKRTF, PKSTF, and TKSTC). The experiment employed a randomized complete block design with three replications. Each race of Pgt was used separately to evaluate the genotypes.

Phenotyping and analysis of variance (ANOVA) revealed significant phenotypic diversity among wheat genotypes for the measured resistance components (infection type and latent period). Cluster analysis classified the wheat genotypes into three main groups: resistant, susceptible, and moderately resistant to moderately susceptible. Among the wheat genotypes studied, 11 genotypes (35%) exhibited susceptibility to all races, while four genotypes (G1, G2, G3, and G17) (13%) demonstrated resistance to all races. The remaining 16 genotypes (52%) showed moderately resistant to moderately susceptible (specific reaction) responses. The biplot analysis (GGE biplot) identified genotype G17 as the most resistant genotype with a uniform response to all races.

Genotypes with varying degrees of resistance to Pgt races identified in this study can serve as new and sustainable sources of resistance for breeding wheat cultivars with a broad genetic basis of resistance. The use of more races and differential isogenic lines can make it possible to provide more specific conditions to identify the effective resistance genes in each genotype more accurately. Evaluating the resistance of the examined genotypes at the adult plant stage can also lead to the identification of resistance genes at the adult plant stage which are more important than the seedling stage resistance genes. The existence of resistance genes at adult plant stage is not far from expected even if the genotype is sensitive in the seedling stage. It is hoped that the correct, and planned use of effective resistance genes at the seedling stage and adult plant stage together will lead to the creation of new stable resistant varieties.