EFFECTS OF ENVIRONMENTAL-FACTORS ON TELIOSPORE GERMINATION, BASIDIOSPORE FORMATION, AND INFECTION OF XANTHIUM-OCCIDENTALE BY PUCCINIA-XANTHII

The effects of temperature, dew, high relative humidity, and light regimes on teliospore germination, basidiospore production and germination, and infection of Noogoora burr (Xanthium occidentale) by Puccinia xanthii were examined. The optimum temperature for the germination of teliospores was between 20 and 30 C, and the optimum temperature for the production and germination of basidiospores was 20 C. The total number of basidiospores produced increased as the period under conditions of high relative humidity was increased. The highest levels of infection were observed at temperatures of 20 and 25 C. No infection occurred on plants not subjected to dew. A dew period of 2-3 h was sufficient to achieve a high level of infection. A period of darkness stimulated teliospore germination under high relative humidity. Light regimes preceded by a dark period had an inhibitory effect on the total number of basidiospores produced. Various light regimes had no effect on the germination of basidiospores and infection of plants.