ВПЛИВ ТЕМПЕРАТУРИ НА РІСТ МІЦЕЛІЮ ЗБУДНИКІВ ХВОРОБ СІЯНЦІВ

В умовах лабораторного експерименту досліджено вплив температури на ріст чистих культур Alternaria alternata, Ilyonectria radicicola, Fusarium oxysporum, Thanatephorus cucumeris, Pythium acanthicum, Phytophthora cactorum, Ph. plurivora, Ph. lacustris, Ph. gonapodyides, які є збудниками хвороб сіянців у лісових розсадниках на території Бескид. Для цих патогенів встановлено діапазони температур, за яких розвивався їх міцелій, зазначено оптимальні температури, за яких розвиток відбувався найшвидше.

Pythium spp. Associated with Rooibos Seedlings, and Their Pathogenicity Toward Rooibos, Lupin, and Oat

Rooibos (Aspalathus linearis) is an important indigenous crop in South Africa. Oomycetes are a common problem in rooibos nurseries, causing serious losses, but limited information is available on the species involved. Molecular and morphological analyses of 117 oomycete isolates from 19 rooibos nurseries and 33 isolates from 11 native rooibos sites revealed the presence of several Pythium spp., including Pythium acanthicum, P. irregulare, P. mamillatum, P. myriotylum, P. pyrilobum, P. cederbergense, and Pythium RB II, and Phytophthora cinnamomi (native site). Most of the species were identified in nurseries and native rooibos, with Pythium irregulare being the most common species occurring in all nurseries and 46% of the native sites. Phylogenetic analyses of the internal transcribed spacer region of the P. irregulare isolates showed that isolates within this species complex fit into three subclades, of which only two have previously been reported. On rooibos, all species except P. acanthicum and the previously characterized P. cederbergense and Pythium RB II were pathogenic and highly virulent. On lupin and oat, rotation crops in nurseries, the three aforementioned species were also nonpathogenic. All the other oomycete species were pathogenic on lupin but less so than on rooibos. On oat, only P. irregulare, P. myriotylum, and P. pyrilobum were pathogenic. This is the first report of P. mamillatum, P. pyrilobum, and P. myriotylum as pathogens of lupin, and P. irregulare and P. pyrilobum as pathogens of oat. The three nonpathogenic Pythium spp. were able to significantly reduce disease caused by pathogenic species in the less susceptible lupin and oat but not on rooibos. On lupin, the nonpathogenic species enhanced the virulence of Phytophthora cinnamomi.

Pythium species in 13 various types of water bodies of N-E Poland

<em>Pythium</em> species and environmental factors in various types of water bodies (2 springs, 2 rivers, 3 ponds and 6 different trophic lakes) were studied. Samples of water were collected every two months (springs, rivers, ponds) and every three months (lakes) in the years 1996-1999 for hydrochemical analysis and in order to determine the Pythium species content. From springs rivers and ponds collected were also ice blocks for determinations of presence of <em>Pythium</em> species. Buckwheatand hemp-seeds, cellophane and snake exuviae were used as bait. Forty-five species of <em>Pythium</em> were found in various types of water bodies. <em>Pythium acanthicum</em>, <em>P. complectens</em>, <em>P. complens</em>, <em>P. diameson</em>, <em>P. dissimile</em>, <em>P. elongatum</em>, <em>P. lucens</em>, <em>P. megalacanthum</em>, <em>P. nagae</em>, <em>P. oedochilum</em>, <em>P. oryzae</em>, <em>P. palingenes</em>, <em>P. periilum</em> and <em>P. polysporum</em> were recorded for the first time in Poland. The largest mean number of species was observed in spring Cypisek, a bit fewer in spring Jaroszówka and lake Białe (oligotrophic-like waters). The lowest mean number of <em>Pythium</em> species was noted in pond Akcent and Pałacowy (polytrophic waters). In all types of water bodies the higest mean number of species was found in winter, and the lowest in summer.

Pythium acanthicum. [Descriptions of Fungi and Bacteria].

A description is provided for Pythium acanthicum. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts.

Effects of Trichoderma on sexual reproduction of some species of Pythium and Phytophthora

Pythium and Phytophthora cultures were subjected to volatile products from cultures of several Trichoderma spp., as well as to killed mycelium and extracts therefrom. Oospores were produced by Pythium acanthicum and P. arrhenomanes and by one strain of each of the compatible heterothallic pairs of P. sylvaticum and P. catenulatum tested, only in the presence of a suitable sterol. The volatile products of the Trichoderma spp. tested had no apparent effect on oospore production. Direct contact with Trichoderma mycelium, or fat-solvent extracts of such mycelium, resulted in oospore production by P. acanthicum. Such oospore production was likely due to the presence of sterols in the Trichoderma. Similarly, with the compatible pairs of Phytophthora cinnamomi tested, oospores were produced by paired cultures or, in some cases, by the 'A2' strains alone, only in the presence of a suitable sterol, whether or not volatile products from Trichoderma cultures were provided to the growing organisms.

The ultrastructure of sexual reproduction in Pythium acanthicum

The young oogonium and young antheridium in Pythium acanthicum Drechsler are densely and randomly packed with numerous mitochondria, dictyosomes, nuclei, interlocking vacuoles of several types, some of which contain a dense storage body, a variety of vesicles, endoplasmic reticulum, and cytoplasmic ribosomes. Wall vesicles, evenly distributed next to the plasma-lemma in rapidly growing oogonia, become localized in groups at points where they appear to initiate the hyphal tip-like development of the oogonial spines. They are also found on both sides of the antheridium−oogonium contact zone. Spine development starts shortly after antheridium−oogonial contact is made and ceases with entry of antheridial material into the oogonium. Excess nuclei, mitochondria, and various organelles are abandoned in the periplasmic space, where they normally quickly disintegrate when the oospore is formed. The periplasmic space is invaded frequently by vegetative hyphae originating outside of the oogonium.