Screening of Lentil Genotypes against Highly Aggressive Strain of Fusarium oxysporum f. sp. lentis

Lentil is one of the most nutritious pulse crops known as masur and grown as a rainfed crop throughout the world in winter season. It is rich in protein, starch, micronutrients and dietary fiber. In the global scenario, India ranked first in the area and second in the production with Bihar being one the major lentil growing state. The majority of the lentil crop is grown in Tal area of the state. As it is cultivated as a rainfed crop, it gets severely affected by several biotic and abiotic stresses. Among the biotic stresses, Fusaium wilt, caused by Fusarium oxysporum f. sp. lentis (Fol) is one of the major fungal diseases and remarkably causing severe crop damage from vegetative to reproductive stage producing significant yield reduction. Fol isolate exhibit great variability and aggressiveness based on agro- climatic conditions. AGLF-11 isolate of Fol collected from Tal area of Bihar was found to be highly aggressive based on previous studies. For this, 50 diverse genotypes were screened against this isolate under greenhouse condition, out of which 14 genotypes showed high susceptibility, 29 genotypes showed moderate susceptibility, 5 genotypes exhibited moderately resistance and only 2 genotypes (L 7920 and DPL 58) exhibited resistance reaction.

IDENTIFICATION OF SOURCES OF RESISTANCE TO Meloidogyne enterolobii IN ACEROLA1

ABSTRACT In Brazil, acerola trees infested by Meloidogyne enterolobii present lower yield and fruit quality. The use of rootstocks resistant to this pathogen is one of the alternatives to overcome this problem. This study aimed to assess the reaction of 22 acerola accessions to M. enterolobii, aiming to identify at least one resistant rootstock. The experiment was carried out in a randomized block design with 10 replications and each plot consisting of 10 plants. Each plant was inoculated with 350 eggs and second-stage juveniles of M. enterolobii, with the gall index (GI) and reproduction factor (RF) being determined after 90 days. The variables were analyzed using the mixed model methodology (REML/BLUP). The accessions ACO-13, ACO-14, ACO-18, and BRS Apodi stood out with four to six plants showing resistance reaction to the root-knot nematode, but the assessment of accessions should be performed under a higher density inoculum and longer time.

Assessment of potentiality of known bacterial blight resistant genes against Xanthomonas oryzae pv. oryzae pathotypes exist in Bangladesh

Bacterial blight (BB) caused by X. oryzae pv. oryzae is a destructive disease of rice and causes 30-50% losses to rice depending on the outbreak. Development BB resistant rice varieties have long been considered as one of the most effective approach to control the disease. However, the durability of host resistance is breaking down due to the change of pathotypes of X. oryzae pv. oryzae globally. Pathotypic analyses of 239 X. oryzae pv. oryzae Bangladeshi isolates on Near Isogenic Lines (NILs) containing resistance (R) gene (s) revealed the existence of eight pathotypes of X. oryzae pv. oryzae. Among eight pathotypes, pathotypes IV and V were considered as major comprising maximum number of isolates, (30.13% and 23.01%, respectively), whereas pathotype VIII considered as minor consisting only 2.51% of total isolates. Pathotype, I showed highest virulence or aggressiveness compatible with all NILs, whereas pathotype VIII exhibited lowest virulence to these NILs. Bacterial blight resistant genes viz. Xa1 (75.00%), Xa11 (62.50%) and Xa21 (50.00%) showed resistance to most of the pathotypes while Xa4 performed worst as compared to all others R-genes. In pyramid lines, IRBBB63 (Xa5+Xa7+Xa13) and IRBB57 (Xa5+Xa7 +Xa21) showed resistance reaction and IRBB61 (Xa4+Xa5+Xa7), IRBB60 (Xa4+Xa5+Xa13+Xa21), IRBB54 (Xa5+Xa21), and IRBB53 (Xa4+Xa21) showed susceptible reaction to X. oryzae pv. oryzae pathotypes. These results collectively indicated the deployment of Xa1, Xa11, Xa4, Xa5, Xa7, Xa13 and Xa21 either alone or in combination against BB would be a best choice for the development of BB resistant rice varieties in Bangladesh.

Assessment of physiological races of Exserohilum turcicum isolates from maize in Argentina and Brazil

Northern corn leaf blight (NCLB) is one of the most important diseases in maize worldwide. It is caused by the fungus Exserohilum turcicum, which exhibits a high genetic variability for virulence, and hence physiological races have been reported. Disease control is based mainly on fungicide application and host resistance. Qualitative resistance has been widely used to control NCLB through the deployment of Ht genes. Known pathogen races are designated according to their virulence to the corresponding Ht gene. Knowledge about of E. turcicum race distribution in maize-producing areas is essential to develop and exploit resistant genotypes. Maize leaves showing distinct elliptical grey-green lesions were collected from maize-producing areas of Argentina and Brazil, and 184 monosporic E. turcicum isolates were obtained. A total of 66 isolates were collected from Argentina during 2015, 2018 and 2019, while 118 isolates from Brazil were collected during 2017, 2018 and 2019. All isolates were screened on maize differential lines containing Ht1, Ht2, Ht3 and Htn1 resistance genes. In greenhouse experiments, inoculated maize plants were evaluated at 14 days after inoculation. Resistance reaction was characterized by chlorosis, and susceptibility was defined by necrosis in the absence of chlorosis. The most frequent race was 0 in both Argentina (83%) and Brazil (65%). Frequencies of race 1 (6% and 24%) and race 23N (5% and 10%) were very low in Argentina and Brazil, respectively. The high frequency of race 0 isolates provides evidence that qualitative resistance based on the tested Ht genes is not being used extensively in Argentina and Brazil to control NCLB. This information may be relevant for growers and breeding programs as the incidence of NCLB is increasing in both countries.

Identification of redgram resistant genotypes and morphological bases of resistance to pod fly, Melanagromyza obtusa (Malloch)

Screening of 49 redgram genotypes conducted to identify pod fly resistant genotypes and morphological basis of resistance to pod fly revealed consistently resistance reaction of ICP 8864 (mean PSI 3.0) and VRG–59-1(mean PSI 3.3) to redgram pod fly. Pod length of various redgram germplasm ranged between 3.55 and 4.84 cm. Pod width ranged from 0.64 to 1.28 cm. Pod wall thickness ranged from 0.21 to 0.43 mm. Trichome density ranged between 302 and 375 per 9 mm2. Redgram pod width was the important morphological factor that influenced the redgram pod fly seed damage to a tune of 34.2 per cent. Pod length and width were positively correlated with the redgram pod fly seed damage while pod wall thickness and trichome density were negatively correlated. However, relationship between pod width and seed damage only was found to be significantly positive and rest of the morphological factors were not significant.

Epigenetic and Metabolic Mechanisms in Plant Resistance to Root-Knot Nematodes

Two wild-type field populations of root-knot nematodes (Mi-Vfield, Mj-TunC2field), and two isolates selected for virulence in laboratory on resistant tomato cultivars (SM2V, SM11C2), were used to induce a resistance reaction in tomato to the soil-borne parasites. Epigenetic and metabolic mechanisms of resistance were detected and compared with those occurring in partially or fully successful infections. The activated epigenetic mechanisms in plant resistance, as opposed to those activated in infected plants, were detected by analysing the methylated status of total DNA, by ELISA methods, and the expression level of key genes involved in the methylation pathway, by qRT-PCR. DNA hypo-methylation and down-regulation of two methyl-transferase genes (CMT2, DRM5), characterized the only true resistant reaction obtained by inoculating the Mi-1.2-carrying resistant tomato cv Rossol with the avirulent field population Mi-Vfield. On the contrary, in the roots into which nematodes were allowed to develop and reproduce, total DNA was generally found to be hyper-methylated and methyl-transferase genes up-loaded. DNA hypo-methylation was considered to be the upstream mechanism that triggers the general gene over-expression observed in plant resistance. Gene silencing induced by nematodes may be obtained through DNA hyper-methylation and methyl-transferase gene activation. Plant resistance is also characterized by an inhibition of the anti-oxidant enzyme system and activation of the defence enzyme chitinase, as opposed to the activation of such a system and inhibition of the defence enzyme glucanase in roots infested by nematodes.

Performance of Some Promising Rust Resistant Bread Wheat Genotypes Under Rain-fed Conditions

The current study was conducted to evaluate the performance and behavior of eight promising wheat genotypes produced by different breeding programs as comparing with the local wheat cultivars under rain-fed conditions at the experimental field of the College of Agricultural Engineering Sciences, University of Sulaimani in Bakrajo during two crop seasons 2014 to 2016. The experiments were laid out according to a randomized complete block design with three replications. Seeds were cultivated at a rate of 140 kg/ha in rows within plots. Host reactions of the tested genotypes with the pathogen population of Puccinia striiformis f. sp. tritici were also investigated under natural infection conditions at the same field. Results revealed high significant differences among the genotypes in term of all the studied traits. Charmo significantly surpassed all other genotypes in stem width (4.90mm), number of kernels per spike (58.41) and grain yield (3856.06 kg h-1), the higher value of grain weight (46.59g) was detected in Azmar 2, while the higher amount of spike per square meter (586.6 spike) was produced by the genotype Shaho2. Azmar2 significantly surpassed all other genotypes in spike length (12.7cm) and leaf area (48.51cm2) while the highest plant height (110.1cm) was detected in Maaroof. Based on the disease severity and coefficient of infection of the genotypes to yellow rust disease, Maaroof, Shaho and Azmar explored high disease resistance reaction and coefficient of infection, while SaberBeg, Aras and Adana showed high susceptibility to the disease.

Reactions of Soybean Germplasm Accessions to Six Phakopsora pachyrhizi Isolates from the United States

Soybean rust, caused by Phakopsora pachyrhizi Syd. & P. Syd., is one of the most economically important foliar diseases of soybean. Resistant cultivars could reduce yield losses and management costs but considerable pathogenic diversity exists among populations of the fungus; thus, resistance to a range of pathotypes is essential. Seedling and detached-leaf assays were conducted to characterize the resistance of 55 soybean plant introductions (PIs) to six purified isolates of P. pachyrhizi originating from the southern United States. In the greenhouse resistance assays, the differentials Hyuuga (PI 506764) and PI 471904 and accessions PI 224268, PI 567025A, PI 567039, PI 567046A, and DT 2000 (PI 635999) were resistant to all six isolates, including Florida isolates from 2011 and 2012 that were able to defeat resistance conditioned by the Rpp1 through Rpp4 genes. Twenty-six other PIs were resistant to four or five of the six isolates. In the detached-leaf assays, eight accessions developed reddish-brown reactions to all six isolates, with an average of only 0.23 to 0.55 uredinia/lesion. These included Hyuuga, DT 2000, two differentials with a resistance allele at the Rpp5 locus, and accessions PI 224268, PI 423960B, PI 567025A, and PI 567046A. Many of the resistant accessions have subsequently been reported to have a resistance allele at the Rpp3 locus, and two others have resistance genes at the Rpp4 or Rpp6 locus. This study provided new information about resistance reaction phenotypes that can be useful for understanding mechanisms of resistance, which Rpp genes and alleles could be combined to obtain broader and more durable rust resistance in soybean cultivars, and pathotype diversity among the six isolates used.