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.

Fine mapping of a new common bean anthracnose resistance gene (Co-18) to the proximal end of Pv10 in Indian landrace KRC-5.

KEY MESSAGE: Mapping and fine mapping of bean anthracnose resistance genes is a continuous process. We report fine mapping of anthracnose resistance gene Co-18 which is the first anthracnose gene mapped to Pv10. The discovery of resistance gene is a major gain in the bean anthracnose pathosystem research. Among the Indian common bean landraces, KRC-5 exhibit high levels of resistance to the bean anthracnose pathogen Colletotrichum lindemuthianum. To precisely map the anthracnose resistance gene, we used a Recombinant Inbred Line (F2:9 RIL) population (KRC-5 × Jawala). The inheritance test revealed that KRC-5 carries a dominant resistance gene temporarily designated as Co-18. We discovered two RAPD markers linked to Co-18 among 287 RAPD markers. These RAPD markers were eventually developed into SCARs (Sc-OPR15 and Sc-OPF6) and flank Co-18 on chromosome Pv10 at a distance of 5.3 and 4.2 cM, respectively. At 4.0-4.1 Mb on Pv10, we detected a SNP (single-nucleotide polymorphism) signal. We synthesized 58 SSRs and 83 InDels from a pool of 135 SSRs and 1134 InDels, respectively. Five SSRs, four InDels, and two SCARs were used to generate the high-density linkage map, which led to the identification of two SSRs (SSR24 and SSR36) that are tightly linked to Co-18. These two SSRs flank the Co-18 to 178 kb genomic region with 13 candidate genes including five NLR (nucleotide-binding and leucine-rich repeat) genes. The closely linked markers SSR24 and SSR36 will be used in cloning and pyramiding of the Co-18 gene with other R genes to develop durable resistant bean varieties.

Phaseolus vulgaris-Colletotrichum lindemuthianum Pathosystem in the Post-Genomic Era: An Update.

Phaseolus vulgaris-Colletotrichum lindemuthianum is one among the oldest host and pathogen interface. Researchers have taken painstaking efforts across the world for understanding the dialogue during early and late phases of interaction. Collectively, these efforts resulted in the deluge of information that helped the researchers to underpin the interface. The latest molecular biology techniques furnished novel detection methods for the anthracnose pathogen, refined the understanding of pathogen population dynamics, and provided the insights on co-evolutionary common bean resistance and C. lindemuthianum virulence dynamics. One of the important breakthroughs came when the Phaseolus vulgaris and its corresponding anthracnose pathogen (C. lindemuthianum) genomes were decoded in 2014 and 2017, respectively. Availability of both the genomes yielded a significant genomic information that helped bean communities to fine map the economically important traits and to identify the pathogenicity determinants and effector molecules. The interface is in a continuous development as knowledge of the anthracnose resistance genes, their precise physical locations, and the identification of effector proteins; the fungus arsenals are being routinely updated. Hence, we revisited the interface and tried to provide an overview of host pathogen dialogue in the genomic era. Additionally, we compiled the sporadic information on this pathosystem from India and provided its futuristic road map to shape its research in the world and northern India, the major dry bean area in the country.

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.