Histopathology of Seed-Borne Infections - Applied Research Center ...

Introduction 3(Carroll, 1969, 1974; Carroll and Mayhew, 1976a,b; Mayhew and Carroll, 1974)and Wang and Maule (1992, 1994), respectively. Similarly, the histopathology ofseeds affected by bacteria is poorly studied, and the investigations are usuallyconfined to seeds infected by Acidovorax, Burkholderia, Clavibacter, Curtobacterium,Pantoea, Pseudomonas, Rathayibacter, and Xanthomonas.Seed-borne nematodes also occur as seed infestation or seed infection. The lattercauses either seed gall formation (Anguina spp.) or symptomatic or symptomlessinfections.1.3 HISTOPATHOLOGYEver since Cobb (1892; see Royle, 1976) proposed the mechanical theory of rustresistance indicating that morphological features, such as thick cuticle, waxy covering,small stomata, abundant leaf hairs, and upright leaves, might be responsiblefor the resistance of wheat varieties to Puccinia graminis, numerous studies onhistology of infected plant parts, particularly leaves and stems, have been carriedout. This information has been summarized in excellent reviews on (1) histology ofdefense (Akai, 1959; Royle, 1976; Schonbeck and Schlouster, 1976); (2) abilitiesof pathogens to breach host barriers (Dickinson, 1960; Emmett and Parberry, 1975;Dodman, 1979); and (3) physiology and biochemistry of penetration and infection(Flentje, 1959; Alberschein, Jones, and English, 1969; Mount, 1978; Durbin, 1979;Kollattukudy, 1985).Although the first observation on internal presence of the mycelium of Colletotrichumlindemuthianum in cotyledons of seeds of Phaseolus vulgaris was madeas early as 1883, further progress until 1950 was rather slow. It is during the latterhalf of the 20th century and more particularly after 1970 that several comprehensivereports have appeared on the penetration and location of microorganisms in seeds.Early information has been summarized by Baker (1972), Neergaard (1979), andAgarwal and Sinclair (1997).Various histological techniques, e.g., the embryo extraction method initially usedby Skvortzov (1937), whole-mount preparations of seed components (Maden et al.,1975; Singh, Mathur, and Neergaard, 1977), free hand sections, and microtomesections have been used. Microtome sections of weakly, moderately, and heavilyinfected seeds alone provide information on exact expanse of mycelium in seed andalso the effects of host–parasite interactions (Singh, 1983). Although used primarilyin the study of virus infections and in a limited way in the study of fungal infections,transmission electron microscopy (TEM) and scanning electron microscopy (SEM)have yielded valuable information, which certainly surpasses the results of lightmicroscopy.REFERENCESAgarwal, V.K. and Sinclair, J.B. 1997. Principles of Seed Pathology, 2nd ed. CRC Press,Boca Raton, FL.