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

68 Histopathology of Seed-Borne Infections3.4.9 ASTERACEAE (COMPOSITAE) (FIGURE 3.11A TO C)(Borthwick and Robbins, 1928; Vaughan, 1970; Kaul, 1972; Chopra and Singh,1976); Kaul and Singh, 1982)The disseminule or propagule is one-seeded indehiscent fruit known as cypsela.The description of fruit is given with reference to important crop plants.External: Cypsils are straight, slightly or strongly curved (Calendula); pointedat both ends (Lactuca and Guizotia), obconical pointed at basal end and rounded attop (Carthamus and Cichorium), elongate-oblong, compressed roughly four-sidedin cross-section (Helianthus); terete, angled, longitudinally ribbed; white, cream,light to dark brown, black; glabrous, hairy, bristled or barbed; dull or lustrous; fruitscar basal, depressed, straight or oblique, at the top annular ring often present; pappuspresent or absent, when present numerous fine bristles (Lactuca), in place of pappusstiff barbs, papery scales or stubby scales present (Carthamus).Internal: Pericarp of epicarp, mesocarp and endocarp, epicarp one-layered, cellsrectangular or elongated along the long axis of the fruit; rarely, cell ends formingspiny excrescences (Lactuca and Cichorium), with or without pigmented contents;mesocarp — a few or multi-layered — with or without split, schizogenous spacefilled with phytomelanin (Helianthus, Carthamus, and Guizotia), cells thick-walledor thin-walled; thick-walled sclerosed cells uniformly distributed (Helianthus andCarthannus) or occur in fibrovascular strands (Lactuca and Guizotia), hypodermal,three to four layers with calcium oxalate crystals (Cichorium). Endocarp one-layered,thin-walled, inconspicuous.Presence of phytomelanin is of particular interest as it is shown to deter insectpredation in the cultivated sunflower (Carlson and Witt, 1974; Rogers and Kreitner,1983). It is hard and highly resistant to alkali and acids. Little is known about itschemical nature; Vries (1948) and Hegnauer (1977) consider it to be of highlyunsaturated acetylenes in Helianthus and Tagetes. Hegnauer (1977) has suggestedthat such compounds are effective against nematodes and bacteria.Seed Coat: Exotestal, epidermis conspicuous, cells rectangular, tangentiallystretched, radially or obliquely elongated, thin- or thick-walled, thickening, uniformwithout or with pits (Helianthus) or confined to radial walls; striate or wedge-shaped(Cichorium and Lactuca), one or more hypodermal layers also present, stretched,compressed, usually thin-walled, rarely subdermal layer thick-walled (Carthamus).Embryo: Axile, straight, spatulate, cotyledons two, appressed, palisade layerdemarcated on adaxial side; procambial strands differentiated, oil and aleurone grainsas reserve food material.Endosperm: One- or two-layered, cells rectangular covered by thick cuticle, oildrops and aleurone grains present.3.4.10 AMARANTHACEAE (FIGURE 3.12H TO J)(Woodcock, 1931; Kowal, 1954; Taneja, 1981)External: Seeds small to medium, rounded (circular), lenticular, reniform oroblong, cylindrical, usually with a distinct marginal rim, notched, brown to black,