Abstract
Changes in the number of the propagules of Macrophomina phaseoli (Maubl.) Ashby in naturally-infested soils were assayed by the soil plate method in elapse of time after storage at 20C.
In Nagano soil, an average of 9 propagules of this fungus per gram of soil were initially detected, but after 2.5 or 4.17 years' storage, the number was reduced to 4 or 2per g of soil, respectively. The half-life in the soil was calculated at 1.88 years on an average.
In 2 different sugar cane field soils of Okinawa after 3.5 years' storage, 3 or 8 propagules of this fungus were detected, but after 5.75-6 years, this fungus was never detected.
Longevity of M. phaseoli in artificial preparations was also compared by testing viability of 50-100 sclerotia of each isolate of the respective preparations.
Three years after storage, cultured sclerotia of 3 isolates tested were 16-40% viable, and in 4 years, they were 5-8% viable.
In tissue-formed sclerotia, 3 isolates tested were 1-27% viable, after 3 years but another isolate was not viable, although it was 2% viable in 2.25 years.
The soil-formed sclerotia originated from a poor substrate of water agar were 4% viable, but those from PDA were 56% viable after 3 years.
The half-life of cultured, tissue-formed, or soil-formed sclerotia was 1.05, 0.84, or 0.65-3.59 years, respectively.
Sclerotia of M. phaseoli in artificial preparations were different in longevity according to differences of isolates, preparation methods, or nutritional sources.
