First report of leaf blight of garlic (Allium sativum) caused by Stemphylium solani in China

L. Zheng ¹, J. Huang ^1*, and T. Hsiang²

¹ The Key Lab of Plant Pathology of Hubei Province, Huazhong Agricultural University, Wuhan, Hubei, 430070, China
² Department of Environmental Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada

*junbinhuang@mail.hzau.edu.cn

Accepted for publication 08/05/07

Leaf blight of garlic is a destructive disease in Hubei province, China. Symptoms were observed on infected leaves in Dangyang County from autumn 2004 to spring 2007, with the diseased area estimated to be over 7000 ha. Garlic yield was reduced by 30% on average with up to 70% yield losses in some fields (Fig. 1).

Figure 1: Leaf blight of garlic caused by Stemphylium solani in a field in Lianghe, Danyang Count, Hubei Province, China, taken May 2005	Figure 2: Leaf blight of garlic caused by Stemphylium solani showing distinct, small, white lesions

Lesions were initially small and white (Fig. 2), and these enlarged to produce apical necrosis, extending until the leaves withered. Isolations were made onto potato sugar agar (PSA) giving white colonies. The centres turned grey, after 4 days on PSA, the agar became yellow-brown throughout (Fig. 3). Single spores were cultured onto 2% water agar, and pieces of autoclaved filter paper were placed on the agar to induce sporulation. Conidiophores were up to 170 μm long. Conidia were pointed at the swollen apex of each conidiophore, clavate, with 1-3 transverse septa, 2-7 longitudinal or oblique septa, and 34~55×17~27 μm (Fig. 4). The pathogen was identified as Stemphylium solani based on Ellis (1971). Genomic DNA was extracted from three isolates, and sequences of rDNA-ITS were obtained. Comparison with sequences in GenBank showed 99% similarity with S. solani (AF203450).

Figure 3: Colony of Stemphylium solani on potato sugar agar after 7 days at 25 C, becoming grayish (left) and staining the agar yellow brown (right)

Pathogenicity tests were performed by spraying a conidial suspension (1×10⁶ conidia/ml) containing 0.1% Tween-20 until runoff (200 m1 per plant) onto upper and lower surfaces of 20 garlic leaves of seven 14-day-old 20-cm tall plants in the laboratory.  Plants were incubated with a 12 h photoperiod at 25℃ and 90% relative humidity. Five days after inoculation, white spots were observed on inoculated leaves but no symptoms were seen on water-treated control plants. Koch’s postulates were fulfilled by re-isolating S. solani from diseased leaves. Leaf blight of garlic is caused by S. botryosum, S. vesicarium, (Boiteux et al., 1994) or Cladosporium echinulatum (Pal, 1976). In China, only S. vesicarium has been reported as a pathogen of garlic (Shang et al., 1997). To our knowledge, this is the first report of S. solani infecting garlic.

Figure 4: Conidiophore and conidium of Stemphylium solani
showing multicelled transverse and longitudinal septa (Bar=30μm)

References

Boiteux LS, Lima MF, Menezes Sobrinho JA, Lopes CA, 1994. A garlic (Allium sativum) leaf blight caused by Stemphylium vesicarium in Brazil. Plant Pathology 43,412-14.

Ellis MB, 1971. Dematiaceous Hyphomycetes. Kew: Commonwealth Mycological Institute.

Pal AK, Basuchaudhary KC, 1976. A new leaf blight of garlic caused by Cladosporium echlnulatum (Berk) de Vries, from Varanasi, Uttar Pradesh. Current Science 45,739.

Shang HS, Wang SQ, Zuo JZ, Zhao JY, 1997.The causal agent of white spot and rot of garlic bolt. Acta Agriculturae Boreali-occidentalis Sinica 6,73-6. (In Chinese)