Artificial Inoculation Technique Research Articles

Insights into maydis leaf blight resistance in maize: a comprehensive genome-wide association study in sub-tropics of India

BackgroundIn the face of contemporary climatic vulnerabilities and escalating global temperatures, the prevalence of maydis leaf blight (MLB) poses a potential threat to maize production. This study endeavours to discern marker-trait associations and elucidate the candidate genes that underlie resistance to MLB in maize by employing a diverse panel comprising 336 lines. The panel was screening for MLB across four environments, employing standard artificial inoculation techniques. Genome-wide association studies (GWAS) and haplotype analysis were conducted utilizing a total of 128,490 SNPs obtained from genotyping-by-sequencing (GBS).ResultsGWAS identified 26 highly significant SNPs associated with MLB resistance, among the markers examined. Seven of these SNPs, reported in novel chromosomal bins (9.06, 5.01, 9.01, 7.04, 4.06, 1.04, and 6.05) were associated with genes: bzip23, NAGS1, CDPK7, aspartic proteinase NEP-2, VQ4, and Wun1, which were characterized for their roles in diminishing fungal activity, fortifying defence mechanisms against necrotrophic pathogens, modulating phyto-hormone signalling, and orchestrating oxidative burst responses. Gene mining approach identified 22 potential candidate genes associated with SNPs due to their functional relevance to resistance against necrotrophic pathogens. Notably, bin 8.06, which hosts five SNPs, showed a connection to defense-regulating genes against MLB, indicating the potential formation of a functional gene cluster that triggers a cascade of reactions against MLB. In silico studies revealed gene expression levels exceeding ten fragments per kilobase million (FPKM) for most genes and demonstrated coexpression among all candidate genes in the coexpression network. Haplotype regression analysis revealed the association of 13 common significant haplotypes at Bonferroni ≤ 0.05. The phenotypic variance explained by these significant haplotypes ranged from low to moderate, suggesting a breeding strategy that combines multiple resistance alleles to enhance resistance to MLB. Additionally, one particular haplotype block (Hap_8.3) was found to consist of two SNPs (S8_152715134, S8_152460815) identified in GWAS with 9.45% variation explained (PVE).ConclusionThe identified SNPs/ haplotypes associated with the trait of interest contribute to the enrichment of allelic diversity and hold direct applicability in Genomics Assisted Breeding for enhancing MLB resistance in maize.

Evaluation of endophytic colonization and establishment of entomopathogenic fungi against Tuta absoluta (Lepidoptera: Gelechiidae) in tomato plants

Background The tomato, Solanum lycopersicum L., is one of the most important horticultural crops that can be consumed fresh or after being processed worldwide. The tomato leaf miner (Tuta absoluta) is one of the most devastating pest to tomato plants due to its mine-feeding nature in the mesophyll tissue of the plant. Fungal entomopathogens can exist naturally in plants as an asymptote. This study aimed to detect the endophytic colonization of Beauveria bassiana and Metarhizium robertsii within tomato plants via artificial inoculation and their virulence effects on Tuta absoluta. Methods Isolates with the highest percent germination and virulence against T. absoluta were selected for endophytic evaluation within tomato plants by different artificial inoculation techniques. Results This study revealed that, isolates with the highest percent germination and virulent to Tuta absoluta had the potential to colonize tomato plants. The result showed that, the maximum mortality rate (97.5%) of Tuta absoluta larvae was achieved by Metarhizium robertsii isolate K-61 at a concentration of 1x108conidial/ml at 7 days post inoculated. However, the highest cumulative mortality (100%) was recorded by Beauveria bassiana isolate APPRC-27 at 10 days post inoculated through the direct contact method. The highest endophytic colonization was registered by isolate APPRC-27 (76.67%) at 7 days post-inoculated using the leaf spray technique, but it declined to 11.67% after 28 days of inoculated. In the case of the seedling inoculation technique, the highest endophytic colonization was obtained in the root tissues of tomatoes at 28 days of inoculated by isolate K-61. Conclusions This study revealed that the leaf spray inoculation technique was the most effective method, followed by seedling inoculation, for the deployment of Beauveria bassiana and Metarhizium robertsii endophytes in tomato plant tissues. Therefore, virulent Beauveria bassiana and Metarhizium robertsii, are promising bioagents for the control of Tuta absoluta if deployed as endophytes.

Development of artificial inoculation techniques for cavity spot caused by Pythium violae to identify new management strategies

Development of artificial inoculation techniques for cavity spot caused by <i>Pythium violae</i> to identify new management strategies

Endophytic fungi: versatile partners for pest biocontrol, growth promotion, and climate change resilience in plants

Plant-associated endophytic fungi (EFs) are emerging as a promising solution to advancing modern agriculture and fostering environmental sustainability, especially in the face of climate change scenarios. These fungi, either naturally residing in plants or introduced through artificial inoculation techniques, improve agricultural production due to their various roles in protecting and supporting host plants. The majority of EFs serve as natural biocontrol agents for a variety of agricultural pests, such as insects, phytopathogens, nematodes, and weeds. Notably, EFs produce secondary metabolites, trigger immune responses, modify plant defense gene expression, confer host plant resistance and/or tolerance, and regulate pest growth, populations, and survival to combat agricultural pests. Beyond controlling pests, EFs promote optimal plant growth, development, and resilience by aiding in the synthesis of vital compounds such as phytohormones and bioactive metabolites, nutrient acquisition, and fortifying plants against environmental stresses and climatic changes. Moreover, the mostly nonpathogenic nature of EFs, coupled with their high yield potential, environmental safety, and cost effectiveness, positions them as eco-friendly and economically viable alternatives to synthetic agrochemicals amidst rapid climate change scenarios. As a result, the promising horizon of EFs in agricultural production necessitates interdisciplinary study and microbial modulation approaches to optimize symbiotic plant-EF relationships and their potential for improved productivity. This review provides current and comprehensive insights into the practical applications and multifaceted benefits of EFs in pest management, plant growth promotion, and climate change resilience for future agricultural production improvements. The analysis reveals the potential of developing EFs into innovative bioformulations such as biofertilizers, biostimulants, and biopesticides, thereby paving the way for their integration into a sustainable and more resilient future agricultural system.

Evaluation of Fungicides as Protective and Curative Treatments against Canker Disease of Eucalyptus urograndis Caused by Chrysoporthe deuterocubensis in Malaysia

Over the years, Eucalyptus plantations have rapidly expanded in Sarawak, Malaysia, accounting for 19% of the total forest plantation area. In a routine forest health surveillance conducted in 2022 at Sarawak, Malaysia, tree stands of Eucalyptus urograndis (Eucalyptus grandis × Eucalyptus urophylla hybrid) were detected with symptoms of stem canker disease caused by Chrysoporthe infection. Given the limited information on the chemical control of Chrysoporthe stem canker disease, there is a growing need to develop effective chemical control strategies to protect and cure Chrysoporthe infection on E. urograndis trees. Therefore, this study aimed to identify the causal pathogen of this stem canker disease in 7-year-old E. urograndis trees in Sarawak, Malaysia, and evaluate the efficacy of various fungicides as curative or protectant treatments on canker infection using artificial inoculation methods. Fungal isolates were first collected and subjected to molecular identification and pathogenicity analysis. Then, in vitro efficacy tests were evaluated using five licensed fungicides: thiram, prochloraz manganese chloride, copper hydroxide, dimethomorph, and mancozeb. Subsequently, the performance of these fungicides was assessed through preventive and curative field experiments on 10-year-old E. urograndis trees using the artificial inoculation technique. Based on the morphological and phylogenetic analysis of the ITS1/ITS4, β-tubulin 2 (BT2), and the combined ITS1/ITS4 and BT2 sequences extracted from 20 fungal isolates, Chrysoporthe deuterocubensis was identified as the causal pathogen of the canker disease, with isolate CHRY18 recording the highest virulence. The in vitro efficacy tests showed that prochloraz manganese chloride achieved 100% inhibition against C. deuterocubensis at 1.0 mg/mL. In the preventive experiment, thiram significantly inhibited C. deuterocubensis infection, yielding the shortest lesion length (19.40 mm) compared to the non-treated control (47.48 mm) at 20 weeks post-inoculation. In the curative experiment, a significant reduction of 54.7% in lesion length was observed in inoculated symptomatic trees after 20 weeks of post-fungicide treatment with copper hydroxide. In conclusion, this study demonstrated prochloraz manganese chloride, thiram, and copper hydroxide as effective chemical controls of C. deuterocubensis stem canker on E. urograndis.

Aetiology and molecular characterization of the pathogens associated with soft rot disease of Aloe vera (L.) Burm. f.

Soft rot is a devastating disease of aloe and the infected plants developed symptoms of rotting tissues from collar region upwards. Aloe plants artificially inoculated with a Dickeya spp. (reported earlier as the causal agent) at the root zone but did not develop the disease symptoms, eliminating the possibility of pathogen to entering through roots. Besides, a Fusarium spp. was repeatedly isolated from collar regions of the naturally infected plants. Further, it was established that lesions produced due to fungal infection predisposed the subsequent infection of the bacterial pathogen. Sequencing results and phylogenetic analysis based on three partial genes of bacteria (dnaX, icdA and mdh) and fungus (ITS, TEF-1α and RPB-2) confirmed the identity of pathogens as Dickeya zeae and Fusarium falciforme, respectively. An artificial inoculation technique was developed for quick screening of aloe germplasm for resistance of bacterium. Among 40 accessions screened, none was found resistant, however, F. falciforme failed to produce lesion on two accessions (Guj4 and Raj3), consequently making them resistant to soft rot disease upon combined inoculation with both the pathogens. Besides the genetic constituent, rapid rotting was observed at 35 °C but not at and below the 15 °C temperature. In planta, the bacterium concentration increased gradually with the rise of incubation temperature between 15 and 35 °C. The present study suggests possible management aspects of the problem through (i) exploiting host resistance and (ii) escaping post–harvest decay by storing and transporting aloe leaves at temperatures ≤ 15 °C and (iii) avoidance of water stagnation in field.

Field Screening of Maize (Zea mays L.) Genotypes against Turcicum Leaf Blight (TLB) under Artificial Conditions

Background: There are a variety of critical problems facing tropical maize cultivation, such as disease infestation, insect/pest and weed problems. Foliar diseases in particular cause significant losses in agricultural yield. Leaf blight, known as northern leaf blight, is a disease of maize leaves caused by an overgrowth fungus. Therefore, it was necessary to develop sources of resistance to TLB and then a field experiment was conducted to study the performance of 64 (44 test crosses, 11 lines, 4 examiners and 5 assays) During Spring 2021-22 at the Agricultural College Farm, Babatla.&#x0D; Methods: Screening was carried under field conditions by adopting an artificial disease inoculation technique Disease score was recorded at tasseling, 20 DAT and maturity stages by using 1-9 scale.&#x0D; Results and Discussion: At maturity stage 12 crosses, seven lines and one check showed resistant reaction (R); 25 crosses, 4 inbreds, one check showed moderately resistant reaction (MR); 7 crosses, 3 inbreds and one check showed moderately susceptible reaction (MS) and one inbred, two checks showed susceptible reaction (S) under field screening. &#x0D; Conclusion: The lines VL171488-2, VL18828, VL19705-8, VL18142, VL175869, SNL19582-22 and tester LM13 showed resistant disease reaction for TLB pathogen at phenotypic level. These lines can be used in future TLB resistance breeding programmes.

Introgression of the QTL qSB11-1TT conferring sheath blight resistance in rice (Oryza sativa) into an elite variety, UKMRC 2, and evaluation of its backcross-derived plants.

Sheath blight (SB) is the most damaging fungal disease in rice caused by a soil-borne pathogenic fungus, Rhizoctonia solani Kuhn (R. solani). The disease resistance in rice is a complex quantitative trait controlled by a few major genes. UKMRC2 is a newly developed elite rice variety that possesses high yield potential but is susceptible to sheath blight disease indicating a huge risk of varietal promotion, mass cultivation, and large-scale adoption. The aim of our present study was the development of varietal resistance against R. solani in UKMRC2 to enhance its stability and durability in a wide range of environments and to validate the effects of an SB-resistance QTL on the new genetic background. In our study, we developed 290 BC1F1 backcross progenies from a cross between UKMRC2 and Tetep to introgress the QTL qSBR11-1TT into the UKMRC2 genetic background. Validation of the introgressed QTL region was performed via QTL analysis based on QTL-linked SSR marker genotyping and phenotyping against R. solani artificial field inoculation techniques. The QTL qSBR11-1TT was then authenticated with the results of LOD score (3.25) derived from composite interval mapping, percent phenotypic variance explained (14.6%), and additive effect (1.1) of the QTLs. The QTL region was accurately defined by a pair of flanking markers K39512 and RM7443 with a peak marker RM27360. We found that the presence of combination of alleles, RM224, RM27360 and K39512 demonstrate an improved resistance against the disease rather than any of the single allele. Thus, the presence of the QTL qSBR11-1TT has been validated and confirmed in the URMRC2 genetic background which reveals an opportunity to use the QTL linked with these resistance alleles opens an avenue to resume sheath blight resistance breeding in the future with marker-assisted selection program to boost up resistance in rice varieties.

Artificial Inoculation Technique to Produce Web Blight Disease on Mungbean

Artificial Inoculation Technique to Produce Web Blight Disease on Mungbean

Endophytic Beauveria bassiana can protect the rice plant from sheath blight of rice caused by Rhizoctonia solani and enhance plant growth parameters.

Beauveria bassiana, a potential entomopathogenic biocontrol agent, has recently drawn attention worldwide for its other additional beneficial roles such as plant disease antagonist, beneficial rhizosphere colonizer, plant growth promoter and an endophyte. In the present study, endophytic colonizing behaviour of five (5) B. bassiana isolates viz., Bb4, Bb16, Bb25, Bb44 and Bb53 were studied in rice following three (3) artificial inoculation techniques viz., seed treatment, root inoculation and foliar spray and the endophytic colonizing ability were determined by culture-based assay. After B. bassiana inoculation, rice plants were challenged with Rhizoctonia solani and disease incidence and plant growth promotion were assessed. Per cent colonization of rice stems, leaves and roots were influenced by inoculation technique, post-inoculation time (7th, 14th, 21st and 28th dpi) and plant growth medium (sterile soil, non-sterile soil), recorded maximum on 14th-day post-inoculation (dpi) i.e., 96% in stems, 92% in leaves and 28% in roots, whereas, lower colonization was recorded on 7th, 21st and 28th dpi. Whereas, the foliar spray was found best as compared to seed and root inoculation techniques, and maximum fungal recovery was observed in stems and leaves and least in roots. Upon colonization, the physical presence of B. bassiana in rice was localized by light microscopy-based studies. Potential B. bassiana strains with endophytic ability were re-isolated and their identity was determined based on morphometric and PCR-based techniques. Further, the present study also identified several virulent genes viz., BbChit1, Cdep1, Bbhog1 and Bbjen1 and extracellular hydrolytic enzymes viz., α-amylase, cellulase, lipase, pectinase and xylanase secreted by endophytic B. bassiana strains as determinants responsible for establishing the endophytic association in rice. On the other hand, a significant reduction in disease incidence was observed in the endophytic B. bassiana Bb4-, Bb16- and Bb44-inoculated plants as compared to the non-endophytic B. bassiana Bb25- and Bb53-inoculated plants along with enhanced plant growth promotion. This is one of the few studies investigating the colonization of B. bassiana in rice and its promising role as a plant disease antagonist and plant growth promoter in rice.

Field screening and identification of stable resistance sources in wheat germplasm against loose smut disease caused by Ustilago segetum var. tritici

Loose smut (LS) caused by Ustilago segetum var. tritici is an important disease of wheat (Triticum spp.) and accounts for 1-2% annual yield losses in India. The disease can be managed easily with the use of seed treatment with systematic fungicides, however, the application of these fungicides remained limited amongst farmers mainly due to their high price, limited knowledge about seed protectants as well as lack of any visible external symptoms on infected seeds. Additionally, seed dressing with protectants is hazardous to the environment and human health and thus not acceptable in organic wheat cultivation. The most affordable and environment friendly technique to protect wheat crop is to develop varieties that are resistant to loose smut disease. Therefore, research efforts have been made to screen one hundred and ninety-seven wheat genotypes obtained from gene bank (Germplasm resource unit, ICAR-Indian Institute of Wheat and Barley Research) under field conditions for LS disease using artificial inoculation technique. The experiment was laid out in randomized block design with three replications for two consecutive years during 2014-15 and 2015-21016. The results of the field trials indicated that only seventy seven genotypes (39.09 %) showed resistance to loose smut and infection ranged from 0-5% under artificially inoculated conditions. More than 15 % genotypes (31) were found to be immune and 18.78 % (thirty seven) genotypes were highly resistant (HR) and twenty three (11.68%) were identified as susceptible (S) genotypes. There was forty-nine moderately susceptible genotype obtained from the experiment. The results reveled that there are some promising LS resistance lines and could therefore be introduced to wheat breeders for further breeding as well as multi-locational trials for developing disease-resistant cultivars.

High-Density GBS-Based Genetic Linkage Map Construction and QTL Identification Associated With Yellow Mosaic Disease Resistance in Bitter Gourd (Momordica charantia L.).

Yellow mosaic disease (YMD) in bitter gourd (Momordica charantia) is a devastating disease that seriously affects its yield. Although there is currently no effective method to control the disease, breeding of resistant varieties is the most effective and economic option. Moreover, quantitative trait locus (QTL) associated with resistance to YMD has not yet been reported. With the objective of mapping YMD resistance in bitter gourd, the susceptible parent “Punjab-14” and the resistant parent “PAUBG-6” were crossed to obtain F4 mapping population comprising 101 individuals. In the present study, the genotyping by sequencing (GBS) approach was used to develop the genetic linkage map. The map contained 3,144 single nucleotide polymorphism (SNP) markers, consisted of 15 linkage groups, and it spanned 2415.2 cM with an average marker distance of 0.7 cM. By adopting the artificial and field inoculation techniques, F4:5 individuals were phenotyped for disease resistance in Nethouse (2019), Rainy (2019), and Spring season (2020). The QTL analysis using the genetic map and phenotyping data identified three QTLs qYMD.pau_3.1, qYMD.pau_4.1, and qYMD.pau_5.1 on chromosome 3, 4, and 5 respectively. Among these, qYMD.pau_3.1, qYMD.pau_4.1 QTLs were identified during the rainy season, explaining the 13.5 and 21.6% phenotypic variance respectively, whereas, during the spring season, qYMD.pau_4.1 and qYMD.pau_5.1 QTLs were observed with 17.5 and 22.1% phenotypic variance respectively. Only one QTL qYMD.pau_5.1 was identified for disease resistance under nethouse conditions with 15.6% phenotypic variance. To our knowledge, this is the first report on the identification of QTLs associated with YMD resistance in bitter gourd using SNP markers. The information generated in this study is very useful in the future for fine-mapping and marker-assisted selection for disease resistance.

Developing an artificial inoculation technique for screening chickpea genotypes against a Syrian isolate of Chickpea chlorotic stunt virus

Developing an artificial inoculation technique for screening chickpea genotypes against a Syrian isolate of Chickpea chlorotic stunt virus

Susceptibility of apple fruits (Malus x domestica Borkh.) to the postharvest pathogen Colletotrichum fioriniae: cultivar differences and correlation with fruit ripening characteristics

Colletotrichum spp. infections are an increasing threat to the fruit production industry worldwide, as a postharvest disease. Gaining knowledge on the susceptibility of apple fruit cultivars to Colletotrichum species is essential for specific breeding programs aiming to decrease the disease susceptibility of commercial apple cultivars. We investigated fruit susceptibility of nine apple cultivars at harvest and after storage, and studied the relationship of the susceptibility with fruit ripening characteristics. An accurate artificial inoculation technique, by wounding and injecting the spore suspension, was used to consistently follow-up the relative susceptibility symptoms of fruits. The nine apple cultivars studied, cvs. Pinova, Nicoter, Nicogreen, Golden Delicious, Gala, Elstar, Jonathan, Idared and Topaz, showed clear differences in susceptibility to C. fioriniae, main species causing problems in Europe, based on lesion expansion growth rate data. Cultivar Nicoter and Nicogreen were evaluated as less susceptible cultivars, while cv. Golden Delicious and cv. Pinova were classified as high susceptible cultivars. After three months of storage all fruit cultivars showed a higher susceptibility than at harvest. We further explored the link between fruit ripening characteristics and postharvest pathogen developments. Results showed significant higher Brix, ethylene production and respiration and significantly lower firmness and titratable acids after storage, with the extent of these changes being cultivar dependent. The ripening parameters respiration and Brix had a positive and the firmness a negative correlation with the lesion expansion growth rate of C. fioriniae after artificial wound inoculations. These experiments help to give a better insight in the susceptibility of different cultivars. Moreover, our data support the hypothesis that the extent of the necrotrophic fungal development depends on the fruit ripening stage.

Deployment of yellow mosaic disease resistance in mungbean [Vigna radiata (L.) Wilczek] through interspecific hybridization

Mungbean yellow mosaic virus [Urdbean: New Delhi: 2011] Accession no. JQ398669.1, was found to be prevalent in both summer and kharif season causing Yellow Mosaic Disease (YMD) of mungbean. Since similar strain was observed in both the seasons, the short duration interspecific derivative lines of mungbean suitable for summer season were evaluated for YMD resistance in kharif season- a highly favourable environment for YMD epidemics during 2014-2016. Out of fourteen lines showing stable resistant reaction, few lines promising for other economically important traits were selected and again evaluated by whitefly mediated artificial inoculation technique for confirmation of resistance during 2017. The selected promising interspecific derivative lines showed no YMD symptoms except SML 1829. SML 1827 derived from interspecific cross between mungbean and rice bean showed highest yield among all interspecific derivatives. Further, rice bean specific segments were also identified in SML 1827 with SSR markers.

Evaluation of tomato hybrids for resistance to leaf curl virus disease and for high-yield production

The leaf curl disease of tomato (Solanum lycopersicum L.) caused by tomato leaf curl virus (ToLCV) poses a serious production constraint throughout the world. An evaluation for resistance to ToLCV and four horticultural traits was carried out using 10 parents and 45 F1 hybrids during the autumn of 2014–2015. Screening against ToLCV was done under both induced natural disease conditions and whitefly (Bemisia tabaci Genn.)-mediated inoculation, with symptoms ranging from symptomless to very severe infection. Under the natural disease conditions, seven parents and 20 F1 hybrids appeared symptomless until the fruit maturation stage. Using the artificial inoculation technique, six parents and 18 hybrids showed resistance at 60 days post inoculation. The correlation coefficients indicated that breeding for ToLCV-resistant hybrids enhanced total yield, fruit weight and total soluble solids content of fruits under natural disease conditions. Based on screening for resistance to ToLCV and four horticultural traits, we identified 4 tomato hybrids, namely CLN 138A × CLN 138B, CLN 138B × PVB-1, CLN 104 × CLN 154 and CLN 17 × PVB-1 to be favorable for commercial use. These hybrids showed resistance after undergoing the whitefly-mediated inoculation, produced 40% higher yield, and were either superior or at par for fruit weight, TSS and lycopene content when compared to the commercial control under natural disease conditions.

Screening of tomato genotypes against bacterial wilt (Ralstonia solanacearum) and validation of resistance linked DNA markers

Tomato yield losses are mainly caused due to bacterial wilt (Ralstonia solanacearum) throughout the world. The disease management is mainly done through chemicals which lead to health risks. Among non-chemical strategies, development of resistant varieties can be a good alternative. The present study was conducted to screen the fifty seven different tomato genotypes against bacterial wilt using artificial inoculation technique under greenhouse conditions. The plants showing symptoms were examined using ooze test. Morphological and molecular characterization of the bacterial strains isolated from infected plants was carried out and bacterial phylotype I was determined using phylotype-specific multiplex PCR. The bacterial-infected tomato genotypes were categorized into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible, highly susceptible and extremely susceptible lines. Seven tomato genotypes viz.RIL-118, Indam-1004, Arka Samrat, PKM-1, PED, EC-802390, and EC-816105 were found highly resistant to bacterial wilt. These genotypes were also evaluated for plant growth, yield and yield-related traits and fruit quality traits under field conditions. Maximum production (2533 g/plant) was observed for the genotype Arka Rakshak followed by EC816156 (2486 g/plant).while genotype EC815157 (200 g/plant) exhibited lowest production. In addition, fourteen bacterial wilt linked markers were validated for these genotypes where SCAR marker, SCU176-534 was found to be linked with the bacterial wilt resistance significantly. This study will be significant and useful in increasing tomato production and to develop new resistant tomato varieties through marker assisted breeding.

SCREENING OF SUGARCANE CULTIVARS AGAINST COLLETOTRICHUM FALCATUM CAUSING RED ROT DISEASE AND ITS CONTROL WITH DIFFERENT FUNGICIDES UNDER LABORATORY CONDITIONS

Ten sugarcane (Saccharum officinarum L.) cultivars were screened against red rot disease caused by Colletotrichum falcatum under laboratory conditions by artificial inoculation technique. These cultivars were graded under various levels of resistance as well as susceptibility using a standard disease rating scale. Two cultivars i.e. NSG-59 and SPF-244 showed resistant reaction to red rot of sugarcane. Three cultivars i.e. CPF-246, CPF-247 and BF-138 showed moderately resistant (MR) reaction against red rot. Remaining five cultivars showed moderate, susceptible to highly susceptible reaction. The results of in vitro evaluation of seven fungicides at four concentrations (10 ppm, 15 ppm, 20 ppm and 25 ppm) showed that all tested fungicides with all concentrations significantly inhibited the mycelial growth of the pathogen as compared with control. However, the inhibition percentage was increased by increasing the concentrations of tested fungicides. Among fungicides Tilt proved the most effective fungicide by inhibiting linear mycelial growth at all concentrations against of C. falcatum followed Nativo while Metaxyl&amp;Mencozeb was the least effective in terms of retarding fungal growth. The findings of the present study suggested that resistant cultivars may be utilized as a source of resistance and may be more useful as donors in breeding programme aimed at red rot disease resistance and the growth of the pathogen is effected by different concentrations of fungicides may play an important role to manage this disease.

Early response of wheat antioxidant system with special reference to Fusarium head blight stress

Fusarium head blight (FHB) is a destructive fungal disease of wheat (Triticum aestivum L.) that causes significant grain yield losses and end-use quality reduction associated with contamination by the mycotoxin deoxynivalenol (DON). Three winter wheat varieties (‘Vulkan’, ‘Kraljica’ and ‘Golubica’) were screened for FHB resistance using artificial inoculation technique under field conditions. The aim of this study was to examine a relationship between FHB resistance and the effectiveness of enzyme antioxidant system of wheat varieties under different sampling times (3, 15, 24, 48, 96, 120 and 336 hai). In the time-course experiments FHB-resistant variety ‘Vulkan’ showed rapid induction of ascorbate peroxidase (APX) and polyphenol oxidase (PPO) activity in the early stages after infection (3 hai) and it seems that in ‘Vulkan’ FHB-resistance is associated with antioxidative enzymes activity. Moderately FHB resistant variety ‘Kraljica’ showed the higher guaiacol peroxidase (POD) activity and higher H2O2 content after 24 hai, increased malondialdehyde (MDA) content at the beginning of infection (3, 15 hai) while induction of catalase (CAT), APX and PPO was delayed. FHB-susceptible variety ‘Golubica’ involved antioxidant enzymes in defense response much later. Based on our results the activity of antioxidant enzymes (APX and PPO) was more pronounced in ‘Vulkan’ than in FHB-medium resistant variety ‘Kraljica’ and FHB-susceptible ‘Golubica’. The differences in antioxidant response of wheat varieties under Fusarium infestation could be the result of genetic properties.

English

False smut of rice (Oryza sativa L.) caused by Ustilaginoidea virens (Cooke) Takahashi (teleomorph Villosiclava virens) is one of the most common fungal diseases of rice in China. The objectives of the research were: 1) to study the biology of Ustilaginoidea virens, 2) to develop suitable media for inoculum production of U. virens, and 3) to develop an artificial inoculation technique for the study of false smut resistance in rice. Seventy diseased rice samples were collected from seven districts of Guizhou province, China during 2007-2008 and 138 single-spore isolates of U. virens were isolated. Among two inoculation methods applied at 3 rice growth stages of rice variety Gangxiang 707 using spore suspension of U. virens isolate 2008-33-1, conidia injection at late booting stage produced the highest false smut incidence of 50.43%, while conidia spraying during the same stage gave only 34.75% disease incidence. Pathogenicity test of selected eight U. virens isolates on rice variety Zhongyou 177 using the conidia injection at late booting stage, showed that the isolates were different in their aggressiveness in which isolate 2008-11-1 gave the highest virulence score of 9 with the disease incidence of 81.66%, while isolate 2007-48-1 gave the lowest score of 5 with only 15.57% disease incidence. These eight U. virens isolates were further tested on six rice varieties using the same inoculation technique. Most of the rice varieties were either susceptible or moderately susceptible except Fengyouxiangzhan that was highly susceptible to U. virens isolate 2007 -79-1 and Nongfengyou 256 was moderately resistant. When the evaluation was done across all the U. virens isolates, Gangyou 827, Jixiangyou 830 and Fengyouxiangzhan were among the most susceptible varieties with disease incidence of 55.06, 54.79 and 53.50%, respectively, while Nongfengyou 256 varieties showed the lowest disease severity as 23.85%. For the pathogen strain, 2008-33-1 was the most aggressive giving 58.09% disease incidence while the fungal pathogen strain 2008-2-2 gave the lowest of 28.17%. Key words: False smut, rice, colony morphology, fungal characterization, Ustilaginoidea virens.