Strawberry Anthracnose: Histopathology of \u3ci\u3eColletotrichum Acutatum\u3c/i\u3e and \u3ci\u3eC. fragariae\u3c/i\u3e

Ontogeny of the invasion process by Colletotrichum acutatum and C. fragariae was studied on petioles and stolons of the strawberry cultivar Chandler using light and electron microscopy. The invasion of host tissue by each fungal species was similar; however, each invasion event occurred more rapidly with C. fragariae than with C. acutatum. Following cuticular penetration via an appressorium, subsequent steps of invasion involved hyphal growth within the cuticle and within the cell walls of epidermal, subepidermal, and subtending cells. Both species of fungi began invasion with a brief biotrophic phase before entering an extended necrotrophic phase. Acervuli formed once the cortical tissue had been moderately disrupted and began with the development of a stroma just beneath the outer periclinal epidermal walls. Acervuli erupted through the cuticle and released conidia. Invasion of the vascular tissue typically occurred after acervulus maturation and remained minimal. Chitin distribution in walls of C. fragariae was visualized with gold-labeled wheat germ agglutinin. The outer layer of bilayered walls of conidia, germ tubes, and appressoria contained less chitin than unilayered hyphae in planta

A Technique for Processing Undisturbed Marine Sand Sediments and Reconstructing Fabric and Porometry

Study of marine sediment pore fluid pathways and porometry requires careful analysis of the fabric of undisturbed sediment samples. A novel solution to the preservation of the interstitial organic material and the in situ fabric or sedimentary structure is the application, with little modification, of well-established biological techniques employing agar infiltration. The solidified agar preserves fabric during subsequent epoxy impregnation. Once impregnated, porosity of the samples can be measured using image analysis of polished surfaces of the microfabric and/or a gravimetric-volumetric technique. Porosity was about 10% higher with image analysis, apparently because of problems in visualizing carbonates and edges of grains. Tortuosity was measured as a function of pathlength ratios taken in stacked planes of microfabric images. The technique allowed us to detect variability in directional tortuosity as a function of orthogonal pathlength ratios. Three-dimensional stacking of digitally acquired wireframe images of sequential planes through the microfabric allows visualization of long continuous pores, some with 2.6 mm length