Seedborne Infection of Rice by Pyricularia oryzae and Its Transmission to Seedlings

Abstract

Seedborne infection of rice by Pyricularia oryzae and its transmission to seedlings were studied quantitatively with naturally infected seeds of three rice cultivars collected from three locations in Nepal. A linear relationship on a logistic scale was found between panicle symptoms and seed infection, i.e., the more symptoms the higher seed infection. However, healthy-looking panicles and branches of panicles could also yield infected seeds. Postharvest measures such as winnowing and sun-drying significantly reduced seed infection by P. oryzae and filled grains had a lower degree of infection than unfilled grains. Sporulation of P. oryzae was most often confined to the embryonal end of germinating seeds. In contrast, most of the nongerminating seeds had sporulation all over the seed surface. Transmission of P. oryzae from seeds to seedlings, studied under various seeding conditions, showed that the transmission rate was always low. Thus, a seed sample with 21% seed infection resulted in less than 4% seedlings with blast lesions. Seed transmission was found for light covering of the seeds with soil or for moist seeding without covering. Transmission was rarely found when seeds were completely covered, and never in seedlings raised under water seeding conditions. Lower infection frequency was observed in seedlings raised in unsterilized soil than in seedlings raised in sterilized soil. Also, percent recovery of P. oryzae from infected seeds was higher in sterilized soil than in unsterilized soil and declined with time. Seedlings grown under low temperature (15 to 20°C) conditions did not develop blast lesions but when the same plants were transferred to high temperature (25 to 30°C) conditions, blast lesions were detected. This confirmed the latent infection in seedlings by P. oryzae grown under low temperature conditions.

Seed-Borne Fungi Associated with Rice Seeds Varieties in Bongor,Chad Republic

“…This high frequency has been reported in previous studies on the seeds of rice in India (Archana and Prakash, 2013) and Pakistan (Khan, 2000;Javaid et al, 2002 (Khan, 2000;Wahid et al, 2001;Javaid et al, 2002;Nguefack et al, 2007). In this study, Pyricularia oryzae, known for a long time as rice seed borne fungus (Manandadhar et al, 1998) was not isolated from any of the rice varieties, confirming the statement by Lamrani et al, (2013) who found that this fungus was less common on seeds. Aluko (1969) tested rice seed samples for seed borne fungi and indicated the scarcity of this fungus in Nigeria.…”

Rice seedborne infection in southern Spain

“…In the year 2001 P. oryzae was isolated in the 45.5% of the lots of certified seeds from the Marismas cultivars, 36% of Orellana and the 45.5% of Fonsa (Table 1). The presence of P. oryzae in the first two years is was not strange since although one of the channels of transmission of this disease is the seed, the scientific bibliography makes reference to that the habitual measures that receives the grain of rice once collected as the drying to the sun or in mechanical dryer, disqualify inoculum of this present agent in the seed (MANANDHAR et al 1998).…”

“…Despite the appearance of P. oryzae in 2001 in certified sowing seeds as much harvested grains makes you think that in previous years the cause of the absence of the pathogen in seeds was caused by the lack of inoculum or so that the environmental conditions were not the appropriate ones for the development of the disease. Also it is possible to emphasize that the smaller percentage of infection found in certified sowing seeds respecting to harvested grain can be consequence of the mechanical drying that disqualifies part of inoculo of this agent in the sowing seeds (MANANDHAR et al 1998). Although the wind is the main via for conidia dissemination of P. oryzae the seeds also considers an important channel of transmission (LEE 1994;OU 1987) of fytopathogenes fungi when these come from campaigns with a considerable level of inoculum and appropriate climatic conditions for the development of the disease, therefore are advisable to know the fytosanitary state of the seeds before being used for sowing time.…”

“…Both pathogens attack seedling, leaves, knots and panicles, including the seeds, in which the fungus can last several years (ITO 1932;MANANDHAR et al 1998) getting to be a primary source of inoculum (ROBER & PAMALA S. GUNNELL 1992;LEE 1994) in tempered zones (OU 1985). On the other hand, it is known that the absence of foliar symptoms under field conditions do not necessarily means that the seeds are healthy (MANANDHALAR 1998;SUZUKI 1934) this affirmation is specially important at the time of seeds certification's programs which are based on lot of seeds selected on the basis of field inspection.…”

Detection of Magnaporthe grisea in infested rice seeds using polymerase chain reaction

“…Rice blast is predominantly a leaf spot disease but under severe conditions, the panicle and grains can be affected (Ou 1985). Rice blast can become severe if blast susceptible cultivars are grown (Manandhar et al. 1998; Long et al.…”