Histological Studies of Ditylenchus africanus Within Peanut Pods.
Ditylenchus africanus entered the immature pegs and pods of peanut (Arachis hypogaea cv. Sellie) at the peg-connection and subsequently invaded the parenchymatous regions of the hull exocarp and endocarp, and eventually the seed testa. The nematode caused malformations of the cells of infected tissues, cell wall breakage, and cell collapse. The damage appeared to be due to enzymatic activity. In some testae the entire parenchyma region, which aids in protection of the seed, was destroyed. In immature pods, the nematodes moved across the fibrous region of the mesocarp into the hull endocarp. In mature pods, however, the fibrous mesocarp of the hull was lignified and apparently was a barrier to penetration of the inner pod tissues. In late-harvested pods, increased numbers of eggs and anhydrobiotes were found in the hull tissues, and eggs in the seed testa, suggesting the onset of winter survival mechanisms of the nematode.
Differential responses of resistant and susceptible groundnut genotypes at cellular level to Ditylenchus africanus
Summary- Ditylenchus africanus causes cellular breakdown in pod tissue of susceptible groundnut cultivars. The histopathology of this nematode on a resistant genotype was studied using light microscopy and compared with the histopathology of D. africanus on a susceptible genotype. Plants of breeding line PC254Kl and cv. Sellie were propagated in a glasshouse, inoculated with D. africanus at inoculum levels of 2000, 5000 and 7000 nematodes per plant and the pods were collected at 90, 120 and 150 days after planting. In contrast to the susceptible genotype, only a small number of nematodes were observed in restricted areas of the pod tissue of the resistant genotype. Furthermore, the resistant genotype showed neither external symptoms nor cellular breakdown in reaction to D. africanus. According to results of this study, the mechanism of resistance involved may be the inhibition of proper development, migration and reproduction of this nematode, thus preventing it building up to damaging population levels.
Silica in Soils1
Publisher Summary Silica in free and combined forms is a dominant component of the solid material of many soils, and dissolved silica is commonly a major solute of soil solutions. Breakdown of primary silicates, translocation of silica in solution, and deposition of secondary silica-containing substances are involved in the development of soils. Ions essential for the growth of plants are released to the soil solution as silicates weather, and these ions may be held against leaching at exchange sites on other silicates. Silica is absorbed in appreciable quantities by some plants and is returned to the surface of the soil as the plants decay. The nature and transformations of silica and silicates in soil are, thus, fundamental to an understanding of many aspects of soil and plant sciences.