Gladiolus Corm Rot Caused by Sclerotium rolfsii in Argentina

In 2000, rot was observed on Gladiolus sp. corms produced and stored in a production locale of the Province of Corrientes, Argentina. Symptoms were associated with the development of whitish mycelial strands and light brown 0.8- to 1.5-mm-diameter globose sclerotia typical of Sclerotium rolfsii Sacc. The fungus was isolated on potato dextrose agar. Pathogenicity tests were done by placing plugs of agar media containing mycelium and sclerotia on corms previously wounded with a scalpel. The corms were planted in sterilized soil, incubated at 20 ± 3°C, and watered frequently. Wilt symptoms were observed 40 days after planting. Basal leaves turned yellow and crown and corm rot developed. Thirty-eight percent of the plants failed to emerge due to corm rot. The pathogen was reisolated from inoculated corms that had become diseased. Control corms, which had been inoculated with sterile agar plugs, did not become diseased. The causal agent of the disease was confirmed as S. rolfsii. To our knowledge, this is the first documentation of gladiolus rot caused by S. rolfsii in Argentina.

First Report of Root and Collar Rot by Sclerotium rolfsii on Apple Trees in Italy

Sclerotium rolfsii Sacc. (teleomorph Athelia rolfsii (Curzi) Tu & Kimbrough) is a polyphagous, soilborne plant pathogen. In summer 1998, a sudden death of 2-year-old apple trees (Malus domestica Borkh.) cv. Royal Gala grafted on M9 rootstock was observed in an orchard near Rome, Italy. Symptoms were stunted vegetation, leaf chlorosis, and root and collar rot. A fungus identified as S. rolfsii was observed producing sclerotia and whitish mycelial strands on root and collar bark. Isolations from roots and at the margin of subcortical necrosis on the collar consistently yielded S. rolfsii colonies on potato dextrose agar (PDA); sclerotia developed within 7 days. Koch's postulates were fulfilled by inoculating 10 1-year-old apple tree cv. M9 rootstocks, grown in 3.5-liter pots, with an S. rolfsii isolate grown for 1 week on PDA at 25°C. One ground plate per plant was used, placed around collar and main roots. Five control plants were treated with PDA only. Rootstocks were kept in the greenhouse at 26 ± 2°C. Within 2 months, 70% of inoculated plants died, with marked necrosis girdling the collar. The other inoculated plants showed a general decline, with widespread necrosis on collars and main roots. Control plants remained healthy. S. rolfsii was reisolated from collars and roots of symptomatic plants. S. rolfsii has been recorded on apple trees in the U.S., India, China, and Israel. In Italy, it is destructive on several crops, and was recently recorded on walnut (1). This first outbreak of S. rolfsii on apple in Italy may have been favored by exceptionally warm late spring and summer temperatures. Reference: (1) A. Belisario and L. Corazza. Plant Dis. 80:824, 1996.

Genetic variations of ectomycorrhizal fungi: extramatrical phase of Pisolithus sp.

The ability of 28 monokaryons and 78 reconstituted dikaryons of Pisolithus sp. from South Africa to form mycelial strands in association with Pinus pinaster was tested under aseptic and non-aseptic conditions. All monokaryotic and some dikaryotic cultures failed to form mycelial strands either on agar medium or in growth pouches. The remaining dikaryotic cultures showed wide genetic variation in the development of mycelial strands and in the extension of their extramatrical phase. The exploration of the surrounding environment by the extramatrical phase from synthesized Pinus pinaster – dikaryotic cultures of the Pisolithus sp. depended largely upon the type of medium used, being more extensive in soil than on nutrient agar medium. Microscopic observation showed that mycelial strands were formed by aggregations of hyphae. Large central hyphae with disorganized cytoplasm were observed in some strands. The results are discussed in relation to nutrient and water absorption. Key words: Pisolithus sp., Pinus pinaster, genetic, extramatrical phase, mycelial strands.

Morphology, crystallography and origin of needle fiber calcite in quaternary pedogenic calcretes of South Australia

In several calcrete profiles from South Australia, needle-fibre calcite is concentrated in the channels and voids of nodules, hardpans, carbonate silt and platy calcrete. The morphology, spatial arrangements and crystallography of the needle-fibre calcite were determined using scanning and transmission electron microscopy. Needle-fibre calcite is composed of single crystals of calcite containing less than 0 5 wt % Mg. Two distinct morphological classes are evident: (1) small single rods or micro-rods, 1 �m in length and 0.1 �m or less in diameter and (2) larger needle-fibres 2-120 �m in length and 0.5-6 �m in diameter which display a variety of habits including multiple rods and serrated forms. The basic unit for the second group is that of a double rod which may be modified by cementation to other rods, and by epitaxial growth or dissolution. Spatial arrangements of needle-fibre calcite are determined by their association with organic matter. The large fibres form within mycelial strands. Lysis of the strand by rod-shaped bacteria releases the needle-fibres for redistribution in the profile. The micro-rods are calcified rod-shaped bacteria.