New reports of pathogen spectrum associated with bulb rot and their interactions during the development of rot in tulip.

Bulb rot, a highly damaging disease of tulip plants, has hindered their profitable cultivation worldwide. This rot occurs in both field and storage conditions posing significant challenges. While this disease has been attributed to a range of pathogens, previous investigations have solely examined it within the framework of a single-pathogen disease model. Our study took a different approach and identified four pathogens associated with the disease: Fusarium solani, Penicillium chrysogenum, Botrytis tulipae, and Aspergillus niger. The primary objective of our research was to examine the impact of co-infections on the overall virulence dynamics of these pathogens. Through co-inoculation experiments on potato dextrose agar, we delineated three primary interaction patterns: antibiosis, deadlock, and merging. In vitro trials involving individual pathogen inoculations on tulip bulbs revealed that B. tulipae,was the most virulent and induced complete bulb decay. Nonetheless, when these pathogens were simultaneously introduced in various combinations, outcomes ranged from partial bulb decay to elongated rotting periods. This indicated a notable degree of antagonistic behaviour among the pathogens. While synergistic interactions were evident in a few combinations, antagonism overwhelmingly prevailed. The complex interplay of these pathogens during co-infection led to a noticeable change in the overall severity of the disease. This underscores the significance of pathogen-pathogen interactions in the realm of plant pathology, opening new insights for understanding and managing tulip bulb rot.

Characterization of Pre-Breeding Wheat (Triticum aestivum L.) Germplasm for Stripe Rust Resistance Using Field Phenotyping and Genotyping.

Wheat is highly affected by stripe rust disease, particularly under cooler environments, and the losses can reach up to 100 percent depending on the intensity of infection and the susceptibility of the genotype. The most effective method to manage this disease is the use of resistant varieties. In the present study, 192 wheat genotypes were evaluated for stripe rust resistance under field conditions and also in a laboratory using molecular markers. These lines included pre-breeding germplasm developed for rust resistance and some high-yielding commercially grown wheat varieties. Out of 192 genotypes, 53 were found to be resistant, and 29 showed moderate resistance reaction under field conditions, whereas the remaining genotypes were all either moderately susceptible or susceptible. Under controlled conditions, out of 109 genotypes, only 12 were found to be resistant to all the six virulent/pathogenic pathotypes. Additionally, a selection of 97 genotypes were found resistant in field screening and were subjected to molecular validation using the markers linked to major R-genes, viz., Yr5, Yr10, Yr15 and Yr17. Nine genotypes possessed the Yr5 gene, twelve had the Yr10 gene, fourteen had the Yr15 gene and thirty-two had the Yr17 gene. The resistance genes studied in the current study are effective in conferring resistance against stripe rust disease. The genotypes identified as resistant under both field and controlled conditions can be used as sources in stripe rust resistance breeding programs.

Genetic footprint of population diversity and genetic structure of Venturia inaequalis infecting apple (Malus × domestica Borkh.).

Apple scab instigated by Venturia inaequalis impels remarkable losses to apple fruit production. In an effort to comprehend the key mechanisms of evolutionary potential defining V. inaequalis population, 132 isolates of V. inaequalis from five commercial apple orchards were collected and assayed using 14 microsatellite markers. The average diversity was observed within the individuals of populations based on the Shannon-Wieners index (I) and observed heterozygosity (Ho) was average but considerably lower than expected heterozygosity (He). The genetic differentiation based on FST values was revealed as an average measure of divergence between populations and had varying proportions of gene flow and migration among themselves. Analysis of Molecular Variance (AMOVA) revealed that variance (94%) was dispersed across individuals with a significant (6%) variation between populations from different regions. To examine host specialization within the V. inaequalis population, the assignment approach based on K-means of clustering (an unsupervised machine learning approach), revealed that the clustering method supported three clusters at (K = 3) and three major clusters were also observed in Principle Component Analysis (PCA). Additionally, Nei's genetic distance values, pairwise estimates of genetic differentiation, dendrogram using the neighbor-joining and PCoA revealed the random distribution of V. Inaequalis isolates that depicted a high proportion of genotypic diversity within populations and population genetic structure. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03672-2.

First report of Fusarium solani associated with the bulb rot of Tulip (Tulipa spp) in India.

Tulip is an ornamental bulbous flowering crop belonging to the Genus Tulipa and family Liliaceae. It is the first ranking bulbous ornamental plant in the world (Nayeem and Qayoom 2015). They are often the first flowers to witness the bloom in the spring. Kashmir valley is located in northern Himalayas in northwestern region of Indian subcontinent. It is the most alluring and fascinating place all over India and the home of famous "Indhra Gandhi Memorial Tulip garden", the largest tulip garden in the entire Asia. However there are number of constraints in tulip cultivation among which bulb rot occupy a prominent place (Piwoni 2000). Bulb rot is posing problem to all the tulip growers throughout the world (De Hertogh et al. 1983). Rot symptoms were observed on tulip bulbs in field as well as in storage conditions (20-22◦C temperature with a relative humidity of 65%) in the summers of 2018 and 2019 in Shalimar fields of Kashmir. The main disease symptoms are yellow sunken spots on bulbs, purple-yellow coloration of leaves. Causal agent was isolated using tissue bit technique (Pathak 1972) on potato dextrose agar plates which where incubated at 24±2◦C . Single spore technique was used to obtain the pure isolate (Johnston and Booth 1983). The isolate covered the full plate (90mm) in ten days. The colony was dull whitish in color, flat and smooth with concentric ring formation in the culture plate with inner ring having a creamy exudation. The mycelium was septate, branched and hyaline in color and measured 3.50-5.20 µm in width with an average of 4.4 µm. Micro-conidia were hyaline, cylindrical to oval, 0-1 septa and measured 7.50-11.00×2.80-3.75 µm in size. Macro conidia were hyaline with 3-4 septa, fusiform, moderately curved which measured 21.15- 32.00×3.80-4.75 µm in size with an average of 28.50±0.21× 4.30±0.2 µm. On the basis of these morphological and cultural characteristics of the fungus, it was identified as Fusarium solani (Mar.) Sacc.,. To confirm the identity the PCR amplification was carried out for two genes Internal Transcribed Spacer (ITS 1, ITS 4)and Translation Elongation factor1-alpha gene (tef1- alpha) (O'Donnell et al. 1998; White et al. 1990). BLAST analysis of the sequence obtained for both the genes showed 99% homology with F. solani sequences in GenBank and Fusarium -ID databases. The sequences were deposited in the GenBank (Accession No MN611433, MW995477). Pathogenicity test was conducted on variety orange emperor both in laboratory and polyhouse. Bulbs were divided into three sets, (three bulbs per set) one set was given injury and dipped in conidial suspension (106 conidia/ml) for 30 min, another set was kept uninjured and dipped in spore suspension of same concentration, the third set was served as control and dipped in sterilized distilled water. All the respective sets were incubated in a moist chamber maintained at a temperature of 22 ◦C to observe symptoms. The injured ones showed symptoms after 7-8 days of inoculation, whereas the uninjured bulbs showed symptoms after 11-12 days. No symptoms were observed in controlled set. A pot experiment was also conducted to carry the pathogenicity tests. Bulbs were injured with the help of sterile needle and were dipped in conidial suspension (106 conidia/ml) for 30 min (Pastrana et al. 2014). The bulbs kept for control were dipped in sterilized distilled water. Bulbs were then planted in pots maintained at 18◦C. The above ground parts of the inoculated bulbs showed symptoms like stunted growth which gradually turned yellow and did not produced flowers. The bulbs after harvesting were rotten .No symptoms were observed in controlled plants. To fulfill the Koch's postulates the fungal pathogen was re-isolated which was identified as F. solani. The pathogen is reported to cause disease in other crops (Gupta et al. 2012) but to our knowledge and on the basis of literature, this is the first report of F. solani causing bulb rot of tulip in India.