Injury and not the pathogen is the primary cause of corm rot in Crocus sativus (saffron)

Abstract

Fusarium oxysporum has been reported to be the most devastating pathogen of Crocus sativus L., a commercially significant crop that yields the saffron spice. However, most of the pathogen isolations have been done from the diseased tissue, mostly from rotten corms, but no study has been conducted on diseased saffron fields. To fill the knowledge gap, the current study was carried out with the intention of recording the diversity of cultivable fungus species from saffron fields and screening them for pathogenicity towards saffron. The three study locations in Jammu and Kashmir, Srinagar (Pampore), Kishtwar, and Ramban, yielded a total of 45 fungal isolates. The internal transcribed spacer (ITS) of rDNA was used for the molecular identification. ITS rDNA-based sequence analysis classified all the operational taxonomic units (OTUs) into two phyla—Ascomycota (88.88%) and Mucoromycota (11.11%). Moreover, Fusarium (57.77%), Geotrichum (17.77%), Mucor (11.11%), Aspergillus (4.44%), Trichoderma (4.44%), Galactomyces (2.22%), and Colletotrichum (2.22%) all had different total abundances at the genus level. It was discovered that the saffron fields in Srinagar have fewer varied fungal species than the other two selected sites. All of the fungal isolates isolated including Fusarium solani, Aspergillus flavus, Trichoderma harzianum, Fusarium neocosmosporiellum, and Mucor circinelloides were pathogenic according to the pathogenicity test; however, injury to the saffron plant was found to be a must. These fungi were pathogenic in addition to F. oxysporum, which is well documented as a major cause of saffron corm rot diseases in Srinagar, but in the present study, injury was a must for F. oxysporum as well. The percentage disease severity index for both saffron roots and corms varied for each fungal isolate.

Isolation, Identification, and Determination of the Virulence of the Causal Agents of Corm Rot of Saffron (Crocus sativus L.) in Valle de Uco, Argentina

“…Based on the modelled disease progression of the tested Fusarium strains, it was possible to hypothesise the presence of three virulence groups: Group A (LJC10578-LJC10580, more aggressive), Group B (LJC10530, intermediate), and Group C (LJC10528, less aggressive). The variation in virulence among the strains is in accordance with the findings in previous studies [ 13 ] and may have practical implications for saffron growers. The presence of highly virulent strains in propagation materials can pose a risk when introduced to pathogen-free areas, while the mildly aggressive strains may hinder early detection based on symptomatology.…”

“…The presence of highly virulent strains in propagation materials can pose a risk when introduced to pathogen-free areas, while the mildly aggressive strains may hinder early detection based on symptomatology. A comparison of the virulence of these groups with those evaluated in previous studies [ 8 , 11 , 13 , 21 ] could provide valuable insights into the composition of the Fusarium mycoflora associated with saffron corm rot in Valle de Uco, Argentina. In addition, fitting epidemiological models to empirical data can be useful for the comparison of isolates and the prediction of certain parameters, e.g., setting the optimal time for the evaluation of saffron accessions in screening tests for resistance to Fusarium corm rot.…”

“…The severity of the F. oxysporum strains in the soil may vary, and this needs to be validated by data [ 13 ]. Isolating and characterising the Fusarium strains responsible for corm rot is crucial to be able to assess their epidemiological importance and potential as a source of field outbreaks and seedborne inoculum [ 8 ].…”

“…Given the presence of FOG in saffron-producing areas, it is advisable to avoid rotating these fields with ornamental crops such as gladiolus or narcissus, which are known to be hosts of the pathogen. However, the survival ability of the pathogen as a saprophyte [ 13 ] may reduce the effectiveness of crop rotation as a control measure. As a result, alternative approaches, including the use of biocontrol agents, are being considered.…”

“…f. sp. gladioli Massey (FOG) is the causal agent of this disease [ 8 , 12 , 13 ], which has been previously reported in Argentina [ 14 ], although no studies have been conducted since 1997. The pathogen survives in infected corms, plant debris, and the soil, in the form of mycelium, chlamydospores, macroconidia, and microconidia [ 12 , 15 ].…”