Sheath blight disease caused by
Rhizoctonia solani
is a severe limitation of lowland rice productivity in Thailand. Typically, confound symptoms occurring with other sheath diseases caused by
...Rhizoctonia
and
Sclerotium
. To classify these pathogen species, 33
Rhizoctonia
isolates were collected from lowland fields in central and northeast Thailand and identified by using morphological and molecular tools described herein. The isolates were identified as
R. solani
AG-1 IA,
R. solani
,
R. oryzae-sativae
(aggregate sheath spot), and
S. hydrophilum
(stem rot). This is the first report of
S. hydrophilum
associated with complex rice sheath blight diseases in Thailand. According to the pathogenicity test of the KDML105 and Pathum Thani 1 varieties,
R. solani
AG-1 IA isolates were found to be the most virulent strain. Each isolate revealed diverts in morphology and disease severity on rice. The H-06 (from Udon Thani) and K-12 (from Buri Ram) isolates showed the highest AUDPC (1448.24–1681.24 and 1301.84–1383.72, respectively) on tested varieties. One hundred and ninety indigenous lowland rice varieties, along with seven commercial varieties, were screened with both aggressive isolates under greenhouse conditions. Interestingly, 30 varieties appeared resistant (< 20% RLH) to tested isolates. Based on result from our study, therefore, that these varieties may provide a source of sheath blight resistance in Thailand, and prove beneficial for future rice breeding programs.
The present investigation aimed to identify reliable morphological markers that could serve as indicators for
Phytophthora infestans
Mont. resistance in potato germplasm. A total of 86 potato ...genotypes were subjected to genetic diversity assessment using simple sequence repeats, followed by a field trial alongside to evaluate resistance responses and morphological characteristics. Two genotypes (LA CHIPPER and J/95–144) exhibited high resistance to late blight (LB), while four genotypes (BR 6609–7, NO–NOVA, MP/99–406, and CP–4174) displayed moderate resistance. The disease response was juxtaposed DUS characters, thus leading to the identification of critical traits (semi-compact to compact foliage, solid stem, angular stem cross-section, no secondary stem coloration, anthocyanin pigmentation on the stem, smooth tuber skin, and white to creamy tuber flesh coloration). These DUS parameters could be utilized for developing high-yielding, LB-resistant potato cultivars in future breeding programs.
Spot blotch (SB) in barley is caused by the fungal pathogen
Cochliobolus sativus
and considered one of the major constraints to successful barley production. Resistance to
C. sativus
was evaluated, ...using a barley collection of 336 genotypes (AM-2014), at the seedling and adult stages. Seedling resistance was evaluated by using a mixture of 19 virulent isolates in Morocco. Virulent isolates prevalent in Uttar Pradesh were used for phenotyping resistance at the adult stage in India. The AM-2014 panel was genotyped with 9-K single-nucleotide polymorphism (SNP) markers using iSelect Illumina Infinium. Genome wide association studies (GWAS) were carried out using SNP markers, infection responses, disease severity, and area under the disease progress curve (AUDPC). The mixed linear model was employed in TASSEL using principal component analysis (PCA) and Kinship matrix (K) as covariates. Higher SB severity, 82.3 ± 13.5 (mean ± SD), was recorded at the Banaras Hindu University (BHU) compared to 47.6 ± 15.0 at the Narendra Dev University of Agriculture and Technology (NDUAT). Nine QTL,
Rcs-qtl-1H-126.9
,
Rcs-qtl-2H-148.16
,
Rcs-qtl-3H-25.27
,
Rcs-qtl-5H-80.35
,
Rcs-qtl-6H-58.24
,
Rcs-qtl-7H-29.62
,
Rcs-qtl-7H-29.72
,
Rcs-qtl-7H-32.81
, and
Rcs-qtl-7H-34.74
, were detected for SB resistance at the seedling stage. For SB severity at the adult stage, a QTL,
Rcs-qtl-7H-32.81
, was detected at BHU while seven QTL,
Rcs-qtl-2H-91.09
,
Rcs-qtl-3H-145.64
,
Rcs-qtl-4H-14.43
,
Rcs-qtl-6H-6.49
,
Rcs-qtl-7H-114.43
,
Rcs-qtl-7H-151.66
, and
Rcs-qtl-7H-150.36
, were found for SB severity at NDUAT. Three QTL,
Rcs-qtl-4H-18.61
,
Rcs-qtl-4H-67.91
, and
Rcs-qtl-5H-110.25
, were significant for AUDPC of SB at BHU. The QTLs reported in this study are important to advance marker-assisted selection and gene pyramiding of SB resistance in South Asia and North Africa in future.
Information on inoculation methodologies and the phenological stage at which corn is susceptible to infection by
Xanthomonas vasicola
pv.
vasculorum
, the etiological agent of bacterial streak, are ...scarce. The objectives of the work were to model the calibration curve of the bacteria inoculum that allows the evaluation of the physiological damage in corn and determine its inoculation methodology. The calibration curve was obtained by dish counting the inoculum concentration. For the inoculation methodology, three sequential experiments were performed: inoculation method (absolute control, wind friction, steel wool, multi-needles and no injury, on the adaxial and abaxial sides of corn leaves), inoculum concentration (non-inoculated control, absorbances from 0.2 to 0.8 in a spectrophotometer at 580 nm) and phenological stage (non-inoculated control, inoculations via seed, in V
4
, in V
8
, in V
T
and in R
2
). For the disease to express itself, around 1 × 10
8
CFU/mL were necessary. Multi-needle treatments and inoculation without causing injury differed significantly from the others, showing greater severity. Inoculation on the adaxial surface was more severe than on the abaxial surface. The symptoms of the disease started at a concentration of 0.4 and the severity of the bacterial streak was more intense at a concentration of 0.6, not differing from the higher concentration. Regarding the most susceptible phenological phase to the bacteria, the observed incubation period was 72 h and there were significant differences only in relation to the incidence expression. Stage V
8
was considered the most susceptible to infection.
Blister blight caused by the biotrophic fungus, Exobasidium vexans Massee, is the most problematic foliar disease of tea in Sri Lanka. A reliable and accurate method is needed for field assessment of ...severity of the disease for epidemiological studies, formulating disease control strategies and crop improvement programmes. A field assessment key with 0–6 scores was developed for blister blight, considering the lowest (0) and highest (>30%) limits of disease severity observed in the field and different stages of symptom development. The key was validated by six raters, 3 experienced and 3 inexperienced. The field assessment trials made using the key were accurate and precise (R2 > 0.80). The area under the disease progress curve (AUDPC), calculated using the disease severity levels obtained using the assessment key, was used to combine multiple observations of disease progress into a 0–9 susceptible scale. Ascending numbers in the scale represent increasing susceptibility. The new scale was proposed to discriminate blister blight resistance in tea accessions/cultivars in field screening. Screening trials for validation of the susceptible scale, conducted using tea cultivars of known resistance or susceptibility levels and newly developed accessions of tea, at three locations, revealed that the 0–9 scale is simple to apply, offers a fine discrimination of blister blight resistance levels, and allows objective evaluation.
•Blister blight is the most problematic foliar disease in tea (Camellia sinensis).•An assessment method is a prerequisite to identify resistance and quantify crop loss.•Blister blight assessment key and cultivar screening method are proposed.•Host resistance is the most effective and economical means of reducing the disease.
Diseases have emerged as one of the major challenges of Brachiaria production in Africa. Nine Brachiaria cultivars were evaluated for leaf rust, leaf spot and leaf blight diseases and agronomic ...performances in two agro-ecological zones of Rwanda. The relationships between agronomic traits and area under diseases progress curve (AUDPC) were determined using Pearson correlation analysis. Cultivars differed significantly (p ≤ 0.05) for their response to these three diseases. Basilisk, Marandu, MG4, and Xaraes exhibited moderately resistant to resistant response to all three diseases, but Cayman and Cobra were susceptible to leaf rust. Site × cultivar × harvest interaction was significant for diseases and agronomic parameters (p ≤ 0.05). Cultivars also differed significantly for biomass production and dry matter content (p ≤ 0.05). The highest biomass producers were Marandu and Xaraes, and Cayman, Cobra and Piata had highest dry matter content. The AUDPC for leaf rust and leaf spot had negative and significant correlation with biomass yield. Our study concludes a satisfactory level of resistance in Basilisk, Marandu, MG4 and Xaraes to all three foliar disease in Rwanda. We recommend routine surveys for emerging and re-emerging Brachiaria diseases and studies to develop effective management measures against Brachiaria diseases.
Blast disease is one of the most important diseases of rice with the fungus
Magnaporthe oryzae
as the causal agent. This research was carried out to evaluate the blast resistance in aerobic rice ...genotypes in comparison with Iranian lowland rice cultivars as a randomized complete block design by measuring area under the disease progress curve (AUDPC) on 53 rice genotypes with three replications in 2017 and 2018 years. Furthermore, molecular evaluation was done using 30 genes-based markers and linked SSR markers along with 60 random SSR markers. According to the results, aerobic rice genotypes, IR82310-B-B-67-2, IR82589-B-B-114-3, IR82616-B-B-64-3, IR82589-B-B-84-3, and IR82635-B-B-143–1 (ranged from 4.11 to 5.96) and Iranian rice cultivars Nemat, Sange-Tarom and Sepidroud (ranged from 4.46 to 4.72) had the lowest AUDPC, indicating they had the least infection severity during different stages of the experiment. Iranian native rice cultivars showed the most susceptibility, and association analysis via stepwise regression showed a significant relationship between some of the markers and AUDPC. Two gene-based markers of
Pi5
and
Pib
and RM259 were detected in accordance with previous studies, and eight SSR markers (RM12091, RM217, and RM3498 with positive effect along with RM234, RM276 RM1300, RM8007 and RM480 with negative effect) were identified as informative markers in relationship with AUDPC for the first time. RM12091 and
Pi5
had the highest adjusted R
2
, accounting for 30.2% and 25.2% of AUDPC variation, respectively. The most effective identified markers could be considered in marker-assisted selection after final validation using different environments and genetic backgrounds. In addition, the results of this study can help demonstrate the significant potential of aerobic rice genotypes for resistance to blast disease.
Septoria leaf spot, caused by
Septoria lactucae
, is one of the major open-field diseases of lettuce (
Lactuca sativa
) in tropical and subtropical regions. However, there are few available studies ...dealing with the identification of useful sources of resistance to this disease. Here, a genetically diverse collection of 42 lettuce accessions was evaluated for Septoria leaf spot reaction under open-field conditions (natural inoculum) during the rainy season. The experimental design was randomized blocks with three replications (16 plants each). Although no immunity-like source was detected, 21 accessions displayed superior levels of rate-reducing resistance with significant lower Area Under Disease Progress Curve (AUDPC) values, encompassing seven accessions of the ‘Crispy green loose-leaf’, eight of the ‘Crispy purple loose-leaf’, two of the ‘Cos/Romaine’, two of the ‘Loose-leaf super crispy’, one accession of the ‘Butterhead’, and one accession of the ‘Iceberg’ morphotype. A subgroup of nine accessions with the highest levels of field resistance was also inoculated under greenhouse conditions with four
S. lactucae
isolates (collected in distinct geographic areas) in two assays at two distinct phenological stages. The cultivars ‘BRS Mediterrânea’ and ‘Vanda’ displayed lowest AUDPC values at the late vegetative/reproductive phenological phase. The remaining accessions displayed intermediate values of AUDPC, with the exception of the cultivar ‘Rubi’ (control), which exhibited moderate levels of susceptibility. The availability for lettuce breeding programs of genetic sources with higher and stable levels of resistance to
S. lactucae
will enable the development of more adapted commercial cultivars, increasing the sustainability of this crop across Neotropical regions.
Bacterial wilt triggered by
Ralstonia solanacearum
is one of the major devastating diseases causing significant yield reduction in eggplant. F
1
hybrids (18 CARI-1 based F1 hybrids and 12 publicly ...available hybrids/varieties) were evaluated for bacterial wilt resistance, yield, and yield attributing traits. CARI-1 based F
1
hybrids showed superiority in yields, however showed a varied level of resistance to bacterial wilt. Further, inheritance and gene action involved in resistance to
Ralstonia solanacearum
was studied. CARI-1 was crossed with two susceptible parents, Arka Neelachal Shyama and Pusa Purple Long to develop six generations for both the combinations. The genetic control of resistance to bacterial wilt was found to be polygenic in the case of the Arka Neelachal Shyama x CARI-1 derived population. While di-genic with complementary gene action in the case of Pusa Purple Long x CARI-1 F
2
population, however deviation in expected ratios was observed in back cross populations. Generation mean analysis revealed the presence of epistasis. For Arka Neelachal Shyama x CARI-1 derived population, owing to the prevalence of additive × additive non-allelic interaction with a negative sign, delaying of selection to later generations, otherwise inter mating between the selected segregates accompanied by selfing for one or more generation(s) is advised for the aggregation of favorable alleles for enhancement of resistance. Similarly, for Pusa Purple Long x CARI-1 population, the simple selection can be efficient due to the prevalence of additive gene action. The inheritance details accumulated in this study would facilitate the introgression of bacterial wilt resistance into elite commercial genotypes.
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