SOME FACTORS AFFECTING SEXUAL REPRODUCTION OF APHANOMYCES EUTEICHES

Papavizas , G. C, and C. B. Davey . (USDA, ARS, Crops Res. Div., Beltsville, Maryland.) Some factors affecting sexual reproduction of Aphanomyces euteiches. Amer. Jour. Bot. 47(10) : 884–889. Illus. 1960.—Oospores of Aphanomyces euteiches Drechsler were consistently formed in abundance on a medium (SM–2) consisting of mineral salts, D-glucose, thioglycolic acid, Difco “Special Agar-Noble,” and a mixture of amino acids added in proportions found in powdered yeast extract. The isolates of A. euteiches studied differed in their nutritional requirements for sexual reproduction. Isolates 4 and 7 formed oospores abundantly on SM–1 which was smiliar to SM–2 except that DL-glutamic acid was substituted for the amino acid mixture. Isolate 572 did not form oospores on medium SM–1 except when DL-methionine was substituted for thioglycolic acid. Sexual reproduction of isolates 4 and 7 was observed at a wider concentration range of reduced-sulfur-containing compounds than that of isolate 572. Sexual reproduction of the 3 isolates studied was influenced in a dissimilar way by varying concentrations of D-glucose and DL-glutamic acid, or by varying concentrations of D-glucose and of the amino acid mixture. The optimal sugar carbon/amino nitrogen ratio range for sexual reproduction of isolate 572 was about 5–22, whereas that of isolates 4 and 7 was 15–180. The pH range for sexual reproduction was as wide as that for growth. An acid reaction was more favorable than a neutral or alkaline one. The optimal pH range was 4.9–5.4. Vitamins were not essential.     

影响 培养基PH值变化的因素

植物组织培养基的ＰＨ值一旦外植体植入就开始发生改变,直到达到某一平衡点,不同种的植物有其各自的ＰＨ平衡点。用６种植物（ＰｉｌｏｔｕｓｅｘａｌｔａｔｕｓＤｅｓｓｅｘＬｅｈｍ,ＬｅｃｈｅｎｎｕｌｔｉａｆｏｍａｓｕｓＲ．ＢＲ．,ＲｏｓａｃａｎｉｎａＬ．,Ｍｅｌａｌｅｕｃａａｌｔｅｒｎｉｆｏｌｉａ（Ｍａｉｄｅｎ＆Ｅ．Ｂｅｔｃｈｅ）Ｃｈｅｅｌ,ＡｎｉｇｏｚａｎｔｈｏｓｆｌａｔｉｄｕｓＤＣ．,Ｚｉｅｒｉａｃｙ     

GROWTH AND SEXUAL REPRODUCTION OF APHANOMYCES EUTEICHES AS AFFECTED BY THE OXIDATION STATE OF SULFUR

Davey , C. B., and G. C. Papavizas . (Crops Res. Div., ARS, USDA, Beltsville, Md.) Growth and sexual reproduction of Aphanomyces euteiches as affected by the oxidation state of sulfur. Amer. Jour. Bot. 49(4): 400–404. Illus. 1962.—Growth and sexual reproduction of Aphanomyces euteiches Drechs., as affected by the oxidation state of sulfur (S), were studied in synthetic media containing d -glucose, dl -glutamic acid, mineral salts phosphate buffer, and various S sources. Organic and inorganic S sources representing some oxidation numbers (valences) were added to the media at concentrations to provide a range from 0 to 128 mg S/liter. The initial reaction in both liquid and solid media was adjusted to pH 6.2. Liquid cultures were maintained at that pH by periodic adjustment. Oxidized S with oxidation number +6 or +4 was not utilized by the fungus, whereas good growth was obtained in the presence of S with oxidation numbers of 0 or -2. Although differences existed among isolates as to relative rates of utilization of the various S sources, there was complete conformity among isolates as to which sources were utilized for growth. Some isolates did not utilize all available S sources for sexual reproduction.     

GROWTH OF GONIUM MULTICOCCUM IN SYNTHETIC MEDIA1

Nutrient requirements of Gonium multicoccum (strains 7–1 and 7–2) were investigated in detail. Acetate supported, most efficiently growth in both continuous light and dark. Acetate could be replaced with pyruvate or lactate in the continuous light, but not in the dark. Sugars were completely ineffective. Thiamine was required for optimum growth. The addition of B₁₂ reduced lag phase, but it did not change the final yield. As the sole nitrogen source, nitrate, ammonia, and urea were equally effective. Nitrite, arginine, glutamine, and uric acid, supported scant growth. Examination of the major and minor mineral requirements resulted, in an optimal medium. A growth rate as high as 5.8 doublings per day was obtained at 25 C in continuous light.     

SOME SOIL FACTORS AFFECTING VERTICILLIUM WILT OF ANTIRRHINUM

Variations in the application rates of chalk and superphosphate and the omission of all the fertilisers had no visible effect on the incidence of wilt caused by any of the five Verticillium species.
he literature dealing with the influence of soil conditions upon the Verticillium wilt of a wide range of host plants is reviewed. It is shown that the species V. alboatrum, V. dahliae, V. nigrescens, V. nubilum and V. tricorpus vary inter se in their pathogenicity to Antirrhinum majus, and that their infectivity may be influenced by soil treatments. Thus, in pot cultures, the incidence of antirrhinum wilt induced by Verticillium dahliae and V. nigrescens was reduced by increasing sulphate of potash or ammonium sulphate; or by decreasing soil moisture. Very wet soil and heavy dressings of hoof-and-horn were the only conditions under which V. nubilunt and V. tricorpus induced wilt symptoms. Z7. albo-atrunt was the most virulent species tested; none of the soil treatments decreased its pathogenicity.     

影响籼稻体细胞胚胎发生几个因素的研究

以 IR36、IR50、IR52及 IR54等品种的幼穗及成熟种子为材料,研究了蔗糖浓度、2,4-D、NAA、激动素及脱落酸对体细胞胚胎发生、结构的保持及植株分化的影响。6%蔗糖有利于胚性愈伤组织的诱导;3%的有利于胚性结构的保持及植株分化。当培养基中不含2,4-D,而含激动素与 NAA 时,幼穗直接出芽;当不含激动素而含2,4-D与 NAA 时,外植体产生非胚性愈伤组织;当不含 NAA 而含2,4-D 与激动素时,外植体产生胚性愈伤组织。认为,2,4-D与激动素是籼稻体细胞胚胎发生的基本因素,而 NAA 的作用是不明显的。不同外植体(幼穗与成熟种子)的体细胞胚胎发生,对2,4-D 与激动素的反应略有不同,幼穗更为敏感。在继代培养基中,加入低浓度的脱落酸有利于胚性结构的保持。随着继代世代的延续,分化培养中愈伤组织所表现出的绿色生长点状物不能发育成完整植株。     

SOME FACTORS AFFECTING THE TRANSMISSION OF LEAF-ROLL VIRUS BY APHIDS

Datura tatula is a more suitable host than potato for studying the factors influencing the transmission of potato leaf-roll virus by Myzus persicae ; it is more easily infected, provides a better source of virus for feeding aphids, produces symptoms more quickly and over a longer period of the year.
Loughnane's (1943) claim that leaf-roll virus is transmitted by starved aphids that feed for only 5 min. on infected potato plants was not confirmed. The shortest infection-feeding time in which M. persicae aphids became infective was 2 hr.; such aphids did not infect healthy plants in the first 2 days and, when transferred to a series of healthy plants at intervals, infected only few. The ability to cause infections was increased by increasing the length of infection feeding. Aphids fed for many days on infected plants could infect healthy plants in the first 15 min. of test feeding, and they continued to cause infections for long periods.
Aphids became infective more readily when feeding on recently infected Datura tatula , showing only slight symptoms, than on older plants with pronounced chlorosis; similarly, young potato sprouts showing no symptoms were better sources of virus for aphids than older plants showing severe leaf roll.
The differences in severity of symptoms shown by potato plants with leaf roll in the field mainly occur because of differences in virulence of accompanying strains of potato virus X , but isolates of leaf-roll virus were found that also varied in virulence.