Anthocyanin accumulation in garlic cv. Morado induced by Penicillium infection and exposure to abiotic stressors

CAVAGNARO, P. F.; SALINAS PALMIERI, M. C.; MARFIL, C.

Mar del Plata

Congreso; XXIX Reunion Argentina de Fisiologia Vegetal; 2012

Sociedad Argentina de Fisiologia Vegetal

In a previous study, twelve garlic cultivars from Argentina were evaluated for resistance against Penicillium alli, the causal agent of ?green mold disease?. Artificial inoculations were performed by adding a spore suspension of P. alli into a standardized lesion performed in the cloves of each cultivar. Morado INTA was the most tolerant cultivar. Interestingly, all cloves from this genotype developed an intense red pigmentation surrounding the fungal colony, whereas cloves from other cultivars were not pigmented or the pigment was very faint. Here, we characterized the red pigment and evaluated whether red-pigmentation is produced as a specific response to P. alli infection. The pigment was extracted in methanol:HCl (99:1), resolved by high performance thin layer chromatography (HPTLC) and confirmed by high performance liquid chromatography (HPLC). Acylated-glycosylated and glycosylated derivatives of anthocyanins were detected in the crude extract. Acid hydrolysis (using HCl 4M and heating) of the pigment extract resulted in a single band (in HPTLC) or peak (HPCL) in concordance with the cyanidin (aglycone) standard. Thus, one major free-anthocyanin, identified as cyanidin, is responsible for the observed red pigmentation. Additional experiments were carried out to test whether anthocyanin pigmentation may occur in response to other stressors. Infection with P. allii, exposure to UV or visible light, wounding; and combinations of these treatments, were evaluated. Determinations of anthocyanin pigmentation were performed by spectrophotometry of methanol:HCl extracts from the garlic cloves. P. alli infection, alone or in addition to UV and visible light exposure, induced strong anthocyanin pigmentation. However, a synergistic effect (i.e., increased pigmentation compared to the individual treatments) was observed for P. alli infection + UV, and P. alli + visible light. These results suggest that anthocyanin pigmentation of the garlic cloves -although intensively triggered by the fungal infection- is not a specific response to P. alli infection, but rather a broader response to biotic and/or abiotic stresses. Thus, it is unlikely that anthocyanins are involved in garlic resistance against Penicillium.