Blind seed disease

There is no need to stress the economic importance of blind-seed disease of ryegrass. Its severity in districts such as Southland has resulted in such areas in a serious decline in ryegrass seed production, but even the so-called “safe” seed-producing localities such as Hawke’s Bay may in certain seasons have many lowgerminating seed crops.

Infected seed may not differ outwardly from healthy seed, though if infection has taken place at an early stage of seed development, seed may be small .and shrunken. Such shrivelled seed is usually removed in machine dressing. Late-infected seed can, however; be detected only by microscopic examination after removal of the outer husks (paleae).

If seed is fully formed when infected, the fungus seems unable to penetrate deeply and the seed may germinate normally. Infected seed which either falls to the ground during harvesting or is sown in a low-germinating line of seed remains dormant until the following summer. When moisture and temperature conditions are favourable-a time usually coinciding with the flowering of the ryegrass-the fungus sends out small mushroomlike growths (apothecia) which are about Qin. in diameter. These produce spores (ascospores) which are forcibly ejected into the air when ripe and are able to infect flowering heads of ryegrass plants. This stage is called primary infection.