Defence- response in bean roots in not affected by low -phosphate nutrition.

Lilia Alvarez Manrique, Alan Richards and Eva L Soriano B.

Instituto de Investigaciones Químico Biológicas. Universidad Michoacana de San Nicolás de Hidalgo. Apdo. Postal 50-3. Morelia, Michoacán. 58089. MÉXICO.

E-mail: esoriano@zeus.umich.mx

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It is well known phenomena that plants are capable to resist invasion by pathogenic organisms due to resistance mechanism that include biochemical responses. Antibiotic (phytoalexin) accumulation is a quick and efficient response of plants against disease.

It has been reported that in roots that have colonised by mycorrhizal fungi, (MVA) there is an increase in resistance to pathogens, although the cause of such resistance is unknown. The main role of captures phosphate from soils with low levels of phosphate.

The objective of this work was to determine if the defence-response of the tissue was affected by phosphate supply. Phaseolus vulgaris L. cv. Flor de mayo plantlets 5 days old growing in a modified Hoaglands solution with only 9 mg/l potassium phosphate were inoculated with a cell well hydrolizate known to elicited phytoalexin accumulation. Control plants received 85-mg/l potassium phosphates in the nutrient solution.

Results after 4 weeks incubation showed that bean plants grown in solutions with low phosphate level were estimulated to produce phytoalexins after elicitation with cell wall hydrolizate. Plants grown with a normal supply of phosphate in the roots, and they did not accumulate phytoalexins when elicited.

The data suggest that phosphate incorporation to roots is the cause of a better defence response to disease.