Differences in cellular abnormalities induced by the probing behaviors of Empoasca kraemeri (Homoptera : Cicadellidae) on tolerant and susceptible common beans

Cellular abnormalities induced by the feeding behavior of Empoasca kraemeri Ross & Moore were studied in 2 tolerant lines ('EMP 84' and 'EMP 392'), an intermediate ('Porrillo Sintetico') and a susceptible ('Calima') cultivar of Phaseolus vulgaris L. Groups of two 3- to 4-d-old female leafhoppers wer e placed for 3 h in 1 clip cage per plant, each covering 1 cm(2) of fully e xpanded primary leaves, 15 d after planting. Leaf tissues were fixed 48 h a fter this access period and prepared for light and confocal microscopy. Dam age to the leaf lamina in all genotypes included cell emptying and breakage of cell walls, as well as enlarged intercellular spaces in the palisade an d spongy parenchyma. In the main vascular bundle, hypertrophied parenchyma cells plus cells with enlarged nuclei and stained nucleoli were observed. I n general, cellular damage was less severe in the tolerant lines than in th e susceptible genotypes, although more so for EMP 84 than for EMP 392. Morp hometry of autofluorescent tracheary elements showed what seems to be a com pensatory response to leafhopper attack in the tolerant lines. Although con trol leaves from tolerant lines had fewer tracheary elements per vascular b undle after leafhopper feeding, EMP 84 had more tracheary elements in damag ed tissues. Both tolerant genotypes had tracheary elements with larger inte rnal radii, which increased their estimated relative flow rates. The implic ations of cellular damage for the onset of hopperburn, in bean as well as o ther host plants such as alfalfa and potato, and the mechanisms of toleranc e are discussed.