Invasion and Colonization of Pathogenic Fusarium oxysporum R1 in Crocus sativus L. during Corm Rot Disease Progression

Abstract

The corm rot of saffron caused by Fusarium oxysporum (Fox) has been reported to be the most destructive fungal disease of the herb globally. The pathogen, Fusarium oxysporum R1 (Fox R1) isolated by our group from Kashmir, India, was found to be different from Fusarium oxysporum f.sp. gladioli commonly reported corm rot agent of saffron. In the present study, Fox R1 was further characterized using housekeeping genes and pathogenicity tests, as Fusarium oxysporum R1 f.sp. iridacearum race 4. Though Fox R1 invaded the saffron plant through both corm and roots, the corm was found to be the preferred site of infection. In addition, the route of pathogen movement wastracked by monitoring visual symptoms, semi-quantitative PCR, quantitative-PCR (q-PCR), real-time imaging of egfp-tagged Fusarium oxysporum R1, and Fox R1 load quantification. This study is the first study of its kind on the bidirectional pathogenesis from corm to roots and vice-versa, as the literature only reports unidirectional upward movement from roots to other parts of the plant. In addition, the colonization pattern of Fox R1 in saffron corms and roots was studied. The present study involved a systematic elucidation of the mode and mechanism of pathogenesis in the saffron Fusarium oxysporum strain R1 pathosystem.

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

“…In addition, nematodes and rodents have also been reported to attack the corms and cause injury ( Khan and Sharma, 2020 ). Some researchers have reported the infection without injury and by just dipping the corm or germinated roots in the spore suspension ( Palmero et al., 2014 ; Gupta et al., 2020 ; Mirghasempour et al., 2022b ) but the present study and others have reported the infection after injuring the corm artificially ( Gupta and Vakhlu, 2015 ; Wani et al., 2016 ; Wani et al., 2018 ; Zhang et al., 2020 ; Bhagat et al., 2022 ; Luo et al., 2022 ). There are many reports on other plants wherein the screening for pathogenicity is done by injury such as cork oak ( Luque et al., 2000 ), kiwi fruit ( Di Marco et al., 2004 ), grape vines ( Halleen et al., 2007 ), Dendrobium nobile , and Dendrobium officinale ( Sarsaiya et al., 2020 ), potato ( Azil et al., 2021 ).…”

“…Since few taxa and mostly F. oxysporum are associated in causing corm rot disease in saffron (Palmero et al, 2014;Gupta et al, 2020;Mirghasempour et al, 2022a), the isolated fungi in the present study were tested for pathogenicity to screen for pathogenic and nonpathogenic taxa. In our experiments with the previously isolated F. oxysporum R1 (Gupta and Vakhlu, 2015), it was established that it needs injury to invade the plant, and without injury, it cannot cause infection in the laboratory experiments (Bhagat et al, 2022). On similar lines, the pathogenicity was checked by injuring the corm as explained in detail in the Materials and methods section.…”

“…The test was conducted in five different combinations with three replicates of each, and the combinations are tabulated in Table 1 for easy comprehension. For the corm injury, the apical end of corm was injured with autoclaved pipette tip (HIMEDIA, Pipette tips, Neutral color, 0.5–10 μl—CG308-1x1000NO) causing a 10-mm-deep and 2-mm-wide injury ( Bhagat et al., 2022 ). For root injury, the tips of roots were cut 1 cm from the terminal end with sterile scissors.…”

Plant-Pathogenic Fusarium Species

“…In the present Special Issue entitled “Plant-Pathogenic Fusarium Species“ ten research articles have been published concerning pathogens from the Fusarium oxysporum species complex (FOSC) [ 1 , 2 , 3 , 4 ]. Ling et al re-sequenced the genome of F. oxysporum f.sp.…”

“…These preliminary results may pave the way towards using molecular engineering to control the infection process through signalling pathway component management [ 3 ]. Sophisticated imaging techniques ( egfp- tagged quantitative imaging) coupled with quantitative pathogen detection (qPCR) are often deployed to detect the early stages of infection in plant tissues and track the sequential spread of the pathogen in invaded organs, a strategy employed for F. oxysporum R1 identification in saffron roots and corms [ 4 ].…”