Pythium myriotylum, a new pathogen of green beans in Spain

Abstract

In 2001 and 2002, bean plants ( Phaseolus vulgaris cvs Festival and Donna) cultivated on rockwool slabs in two commercial greenhouses in southeastern Spain were observed with root necrosis and necrotic streaks at the base of stems. In one greenhouse a few, scattered plants were affected, while in the other an estimated 20-30% dead plants occurred in distinct clusters. A Pythium sp. was consistently isolated from roots and stems of the affected plants on potato dextrose agar and cornmeal agar amended with pimaricin, ampicillin and rifampicin (P 5 ARP).Single hyphal transfers gave pure cultures of this oomycete. Four isolates from different plants produced filamentous inflated sporangia with zoospores and aplerotic oospores. Sequences of ribosomal DNA from ITS1 region, 5·8S rDNA and ITS2 were identical for all four isolates and that from isolate Py-V3 has been deposited as GenBank Accession No. AM396958. The isolates were identified as P . myriotylum on the basis of molecular sequences and morphological characteristics (Van der PlaatsNiterink, 1981).Phaseolus vulgaris cv. Emerite at the 5-7 leaf stage was inoculated with three isolates (Py-V1, 2 and 3) by irrigating plants with 50 mL of mycelial suspension, per plant, obtained by growing isolates on potato carrot agar (PCA) in 9 cm Petri dishes until they fully covered the surface, then blending and homogenizing mycelium in 300 mL sterile distilled water.The plants were grown in plastic bags filled with perlite and kept in a greenhouse where temperatures varied from 22-31 ° C. After 29 days all plants had necrotic roots, some with stem streaks and some eventually died, similar to the disease development originally observed. Control plants irrigated with sterile distilled water washed-off uninoculated PCA remained healthy. When inoculations were repeated at a lower temperature range (13-30 ° C), isolates Py-290 and Py-V2 caused root necrosis in all inoculated plants but stem streaks and death in only a few. Pythium myriotylum was reisolated from inoculated plants. High temperatures are associated with more severe disease development (Gay, 1969). This is the first report of P . myriotylum as the causal agent of root and stem necrosis of adult bean plants in Spain. References Bioforsk -Norwegian Institute for Agricultural and Environmental Research, Høgskoleveien 7,1432 Ås, NorwayIn 2004 and 2005, several soil surveys were conducted in the main melon ( Cucumis melo ) production areas of Honduras and Guatemala, all areas with a history of vine decline. Fifty-nine samples from twenty different farms were collected from the rhizosphere zone of wilted plants. Samples were analyzed by a baiting method consisting of sowing melon seeds in a mixture of each rhizosphere sample and vermiculite (1:6 vol/vol). Thirty-six melon plants per sample were placed in a growth chamber with a 16-h photoperiod and temperatures of 23 to 25 ° C. Diseased plants started to appear when plants showed one or two true leaves. The first symptom observed was girdling of the lower stem, followed by...

The impact of climate change in the spread of Pythium myriotylum in ginger: a critical review

“…Furthermore, studies have shown that the spread of Pythium myriotylum in ginger is strongly influenced by soil physic-chemical properties [16]. Specifically, changes in soil pH and organic matter content due to climate change can create a more favorable environment for the growth and survival of Pythium myriotylum [17].…”

“…This expansion is characterized by its detection in regions previously considered unsuitable for its survival and proliferation. Recent report showed that P. myriotylum were detected in Shandong, Henan, and Anhu Province of China [2] which has average temperature in summer at 27 o C. Furthermore, the occurrence of P. myriothilum in crops such as hemp [32,33] and green bean [34] highlights its ability to infect a diverse range of plants and potentially cause widespread damage to agricultural systems. The accurate identification and understanding of Pythium species in agricultural environments are crucial for assessing their epidemiological implications.…”