TESTING FOR RESISTANCE TO PLASMOPARA-HALS TEDII IN SUNFLOWER PLANTLETS GROWN FROM IN-VITRO CULTURES OF IMMATURE EMBRYOS

In vitro culture of immature sunflower embryos for rapid fixation of i nbred lines will be of particular interest only if selection is possib le at the same time. This paper presents a methodology to determine re sistance to downy mildew (Plasmopara halstedii) of plants obtained fro m immature embryos. First tests on mature embryos indicated that suspe nsion concentrations between 5 000 and 500 000 zoosporangia/ml all gav e infection levels close to 100%. It was found that seedling age was i mportant, that at the cotyledon stage 3% of plants escaped infection, whereas with 1 or 2 pairs of true leaves, 99.5% of plants were infecte d Passage in a humid chamber for 48 h was observed to be favorable for infection. Trials on plants obtained from immature embryos gave 100% infection with a suspension of 50 000 zoosporangia/ml. It was conclude d that the best method was to spray plants with 1 pair of true leaves with a suspension of 50 000 zoosporangia/ml and then keep them for 48 h in a saturated atmosphere. A breeding programme to introduce downy m ildew resistance and cytoplasmic male sterility using in vitro culture is proposed.