EFFECT OF PHAEOISARIOPSIS GRISEOLA ON CHLOROPHYLLASE ACTIVITY AND CHLOROPHYLL CONTENT OF COMMON BEAN (PHASEOLUS VULGARIS) LEAVES
SF PASCHOLATI and JR STANGARLIN
Department of Plant Pathology, ESALQ/USP, PO Box 9, ZC 13418-900 Piracicaba, SP, Brazil
Background and objectives
Angular leaf spot, caused by Phaeoisariopsis griseola, is an important disease of common bean. It affects photosynthesis by reducing the photosynthetic leaf area due to the formation of necrotic lesions (= visual lesions). In addition photosynthesis apparently can also be affected by increases in chlorophyllase activity that causes chlorophyll losses even in tissue away from the diseased area (=virtual lesions). Thus, we decided to study chlorophyllase activity and chlorophyll content in leaf tissues inoculated with the fungus by sampling visual and virtual lesion areas.
Materials and methods
The bean cultivars Carioca and Rosinha, showing moderate and high susceptibility to P. ;griseola, respectively, were used. Plants were grown inside chambers and after 14 days, a spore suspension of the fungus was sprayed onto the second trifoliate leaves. When symptoms were visible, leaf discs were obtained from the inoculated tissue representing areas with low (5-8%) and medium (18-20%) severity and areas without lesions. Samples were also collected from uninoculated leaves (third trifoliate leaf) from diseased plants. The chlorophyll was extracted in 80% acetone and measured spectrophotometrically while chlorophyllase activity was determined using acetone powder through spectrophotometric measurements.
Results and conclusions
The results showed that in the leaves of the cultivar Carioca, based upon the severity of the disease, there was a reduction of 11-21%, 12-23% and 10-22% in the amount of total chlorophyll and chlorophyll a and b, respectively, in the remaining green area (apparently health) of inoculated leaves. There was no change in chlorophyll content of uninoculated leaves of diseased plants. Chlorophyllase activity was more significant in areas with low and medium severity: 8.0 and 11.4 ;units/g acetone powder. Conversely, leaves from the cultivar Rosinha showed reduction of pigments only in the uninoculated leaves of diseased plants: 9.5%, 10% and 10.5% for total chlorophyll and chlorophyll a and b, respectively. Chlorophyllase activity in those tissues was 14 ;units/g acetone powder equivalent to 55% more activity than in control leaves. The results indicate the presence of virtual lesions in leaves of bean plants inoculated with P. ;griseola.