The sexuality and population structure of Pythium sylvaticum

Abstract

51 : 429-436. 1973. The sexuality and population structure of Sexual characteristics of 36 isolates of Pythi~~nz sylvatic~mz were investigated. Fourteen of 15 heterothallic males were also homothallic while only 2 of 21 females were homothallic. Four male and five female groups of isolates were delineated by similar reacting patterns under five different temperature and light conditions. Mature oospores formed in crosses varied with both male and female isolates and were not correlated with sexual strengths of reacting isolates. Three-to-one ratios of males to all other progeny occurred among 198 single-oospore progeny of two crosses involving non-homothallic parents. Most progeny were also homothallic. A pattern for the distribution of sexual characteristics of natural populations of P. sylvaticrun is proposed based on characteristics of the 36 isolates.

Fertility and Mating Type Frequency in Indian Isolates of Sclerospora graminicola, the Downy Mildew Pathogen of Pearl Millet

“…Michelmore and Ingram (11) demonstrated self-fertility in Bremia lactucae as a form of secondary homothallism and not as a mixture of heterothallic isolates of opposite compatibility types. Such self-fertile isolates have been reported for other heterothallic members of the peronosporales Phytophthora drechsleri (13), Pythium sylvaticum (15), and Peronospora parasitica (22). However, the most detailed studies have been made with Phytophthora drechsleri (13,19) and B. lactucae (11), where genetic and cytological experiments have indicated that the self-fertile isolates are trisomic for the determinants of compatibility type follow-…”

“…In addition, the results show that the frequency of the mating types Mat A and Mat B in populations of S. graminicola was approximately equal, thus providing greater chances of producing progenies with new recombinations of alleles. In other heterothallic oomycetes also, generally only two sexual compatibility types have been identified in an approximate 1:1 ratio (1,10,15,20). Because both mating types were found in approximately equal proportion in India, it indicates that sexual reproduction plays an important part in the evolution of new genetic recombinants and, thus, development of new virulent pathotypes.…”

Expression and Inheritance of Sexual Preference and Selfing Potential inPhytophthora infestans

“…In Achlya bisexualis, for example, heterothallism is based on the existence of discrete male and female strains, rather than on mating types (Raper, 1939). A similar system apparently acts in Pythium sylvaticum, although so-called heterothallic isolates are partially homothallic (Papa et al, 1967;Pratt and Green, 1973). In some other oomycetes, such as Achlya ambisexualis (Raper, 1940), sexuality is also a primary determinant of compatibility although sexuality can be relative, as in Phytophthora.…”

Monitoring virulence and sexual compatibility in Brazilian Bremia lactucae populations

“…This study demonstrates that all isolates of B. lactucae collected in Brazil are self-fertile with secondary homothallism. The same mechanism of reproduction has been reported for other heterothallic members of Peronosporales, such as in the genera Phytophthora, Pythium, and Peronospora (De Bruyn, 1937;Mortimer et al, 1977;Pratt & Green, 1973). Homothallism is common among oomycetes and can differ within genera, as Phytophthora cactorum and Plasmopara halstedii are homothallic, whereas Phytophthora nicotianae and Plasmopara viticola are heterothallic (Abad et al, 2019;Erwin & Ribeiro, 2005;Gascuel et al, 2015;Wong et al, 2001).…”