Application of a New Laboratory Method for the Determination of the Survival of Helminthosporium Sativum Spores in Soil

Abstract

X laboratory tnethod is described for deterriiirli~ig the survival of Iiel~~zirzLl~o-sporiunz sativu~n spores in soil. Xri oil-water emulsion co~itai~ling the spores is mixed with potato dextrose agar supplenle~lted with molasses; tnicro.;cope slides arq. then dipped into the misture, incubated, and esa~nirled for spore germ~nation. ,\pplication of the method showed that viability of spores in '1 dry soil did not decline over a 9-niorith period whereas survival of spore-; in saturated soil dropped ~narkedly in the s~ilne period. Inter~nedi~itc nloisture levels had intermediate eSfects on the spores. Stuciics on spores obtnined directly from cultivated fields indicated little mort,llity fro111 fall to spring. .I summerfallow year between two wheat crops r e s~~l t e d in ' 1 st~\)stallti,~l decline i l l percentage of viable spores.

Survival of <i>Bipolaris sorokiniana</i> (Sacc.) Shoemaker in soil and residue of wheat

“…Survival of B. sorokiniana in soil for different periods has also been reported by other workers from different countries. The survival of the pathogen in soil for 9-20 months depending on soil conditions has been documented by Chinn and Ledingham (1958) and Chinn (1965). Boosalis (1962) observed that the pathogen could survive in soil for more than 16 months • C under 50% moisture holding capacity.…”

Cochliobolus sativus on Barley in Scotland

“…Australian experience is that it can survive on stubble in the soil for at least two years at room temperature (Butler, 1959). In Austraha the fungus produced conidia abundantly on stubble in the autumn and spring, and survival of cotiidia is enhanced in dry soils (Chinn and Ledingham, 1958).…”

Constitutive dormancy in conidia of Bipolaris sorokiniana

“…There may also be a different effect if conidia are indirect contact with soil. Conidia germinated at nearly 100% after recovery from soils maintained at relative humidities of less than 50% for 52 months (Ledingham 1970); after 9 months in saturated soils germination was only 2% (Chinn & Ledingham 1958).…”

“…Even in soil, the addition of nutrient substances overcomes soil fungistasis and conidia germinate (Chinn & Ledingham 1957). In the present study, the evidence indicates that drying initiates dormancy in some B. sorokiniana conidia and that this is overcome by freezing or incubation on moist soil.…”