The effects of heat shock and inoculum density on growth and sporulation in axenic cultures of the flax rust fungus

Abstract

BOASSON, R., and SHAW, M. 1988. The effects of heat shock and inoculum density on growth and sporulation in axenic cultures of the flax rust fungus. Can. J. Bot. 66: 189 -193.The number of mycelial colonies of Melarnpsora lini (Ehrenb.) Lkv. was increased by a 2-h heat shock at 3 1 OC delivered 3 h after uredospores were seeded on a liquid medium at 17 f O.S°C under axenic conditions. At 35 -38 days from seeding, the ratio of the respective number of colonies in shock and nonshock treatments in 125-mL culture flasks was highest (7.5 to 22) at inoculum levels (1 to 4 x lo3 uredospores ~m '~) that yielded about 10 colonies per flask without heat shock; the ratio declined sharply at inoculum levels adjusted to yield either smaller or larger numbers of colonies per flask without heat shock. Sporulation (extinction at 458 nm) and protein per colony were positively correlated; were not directly affected by heat shock; were determined by colony number; increased to maxima as mean colony number per flask increased from 1 or less to from 10 to 100 in different experiments; and decreased at higher colony numbers per flask. The results indicate that heat shock promotes the initiation of colonies; that colony number determines the duration of logarithmic growth; and that increasing competition among individual colonies is the primary factor limiting growth and sporulation, whether or not the uredospore germlings are subjected to heat shock. BOASSON, R., et SHAW, M. 1988. The effects of heat shock and inoculum density on growth and sporulation in axenic cultures of the flax rust fungus. Can. J. Bot. 66 : 189-193. Les nombres de colonies myckliennes du Melampsora lini (Ehrenb.) Lkv. augmente i la suite d'un choc thermique de 2 h, i 31 "C, administrk 3 h aprks l'ensemencement des urkdospores sur milieu liquide i 17 + O.S°C, sous conditions axkniques. De 35 i 38 jours aprks l'ensemencement, le rapport des nombres respectifs de colonies dans les traitements avec choc sur les traitements sans choc en fiole de 125 mL, ktait plus klevks ( 7 3 i 22) avec des densitks d'inoculum (1 i 4 x lo3 uredospores cm-I) qui produisent 10 colonies par fioles sans choc thermique, et diminue rapidement i des densitks d'inoculum ajustkes pour produire des nombres de colonies par fiole plus klevks ou plus faibles sans choc thermique. La sporulation (extinction i 458 nm) et les protCi'nes par colonie montrent une corrklation positive; ne sont pas directement affectks par le choc thermique; sont dkterminks par le nombre de colonies; atteignent un maximum alors que le nombre moyen de colonies passe de 1 ou moins i 10 et B 100 dans diffkrentes expkriences; diminuent avec des nombres plus klevks de colonies par fiole. Les rksultats indiquent que le choc thermique provoque l'initiation des colonies; que le nombre de colonies dktermine la durke de la croissance logarithmique; et qu'une compktition accrue entre les colonies individuelles est un facteur primaire qui limite la croissance et la sporulation, que les sporules soient ou non soumises i un choc the...

Rust of flax and linseed caused byMelampsora lini

“…Later Turel (1973) developed a fully defined chemical medium. Subsequently, it was found that axenic mycelium of M. lini grows best when it is floating on a liquid medium, and a fully defined liquid medium was developed (Boasson and Shaw, 1984, 1988a; Bose and Shaw, 1974a). Bose and Shaw (1974b) reported luxuriant growth of M. lini on liquid media with most colonies producing typical orange urediniospores after 6 weeks with some of these also producing dark brown teliospores after 8 weeks of growth.…”

“…The urediniospores produced were capable of infecting flax plants in a normal manner. Additional studies aimed at improving the efficiency of colony initiation and growth and urediniospore formation established that CO 2 is essential for colony initiation (Boasson and Shaw, 1981), that low temperature (16–17 °C) is a critical requirement for mycelial growth (Turel, 1969b), that a 2‐h heat shock (31 °C) 3 h after urediniospore seeding significantly increases the number of mycelial colonies (Boasson and Shaw, 1988a), that glutamine, citrate and pH can influence growth and urediniospore formation (Boasson and Shaw, 1988b), that calcium ion, aspartic acid and colony density levels influence urediniospore formation (Bose and Shaw, 1974a) and that placing an impermeable membrane such as Parafilm or Saran wrap on the surface of 3‐week‐old mycelial mats for 2 weeks significantly increases (2–4‐fold) urediniospore formation (Boasson and Shaw, 1985). Axenic cultures of M. lini appear to maintain their original dikaryotic nuclear condition and their virulence patterns on flax differential lines even after several generations on defined media (Boasson and Shaw, 1991).…”