Fertile sporophore production of Typhula phacorrhiza in the field is related to temperatures near freezing.
Two field tests and one lab test were conducted to examine the environmental factors affecting sporophore production in Typhula phacorrhiza and to compare these results with those documented for T. ishikariensis and T. incarnata. In the 2001 lab test where lighting, soil moisture, and soil-sand media were tested in 50 mL screw-cap tubes incubated at 4 degrees C, the limiting factor for Typhula sporophore production was found to be moisture. In the fall 2001 field test, 100 sclerotia of six isolates from three Typhula spp. were placed into pots filled with a sand and soil mixture. The pots were monitored weekly, and maximum sporophore production for all six isolates and for watered and unwatered pots was observed at 11 weeks, which was soon after mean daily temperatures fell below 0 degrees C. In the second field test in fall 2003, five isolates of the three species were tested with similar procedures, but peak sporophore production was observed after 6 weeks, and again only after mean daily temperatures fell below 0 degrees C. In the field, sporophore production of T. phacorrhiza seems to require the same environmental cues as those of T. ishikariensis or T. incarnata, namely high moisture and temperatures near freezing.
Snow Mold
In cold-temperate region, plants are more frequently damaged by biotic factors, primarily snow mold, than by abiotic factors such as freezing. Snow mold is used here as a generic name for plant diseases that occur under snow cover. Many different fungi may be involved, and each snowmold fungus has its own ecological and physiological features. They normally infect and can prevail on plants under snow, but generally are dormant during other seasons. Their habitat under snow is characterized by constant low temperature, darkness, and high moisture. Snow mold fungi are, in general, opportunistic pathogens, which, in the absence of antagonists, attack plants depleted of reserve material. Such organisms which not only tolerate cold temperatures but thrive under such conditions are called “psychrophiles.” In the final section of this chapter, ambiguities in the use of the common term “psychrophile” are illustrated, and these are ascribed to the complex life cycles of different fungi. Another term, “cryophile,” may be more appropriate, to denote fungi, including snow mold fungi that prevail in the cryosphere. Dr. Takao Araki who showed NM the significance of field observations and led him to a whole new world under snow; photograph taken circa 1978. © Springer Science+Business Media Singapore 2016 N. Matsumoto, T. Hsiang, Snow Mold, DOI 10.1007/978-981-10-0758-3_1 1 In cold-temperate region, agricultural fields are often covered with snow for more than 4 months, and plant tops look dormant even before snow cover and are yellowed after snow cover. From the point of view of the plant, half of the year is winter. However, despite harsh winter climates in such regions, plant growth is promoted due to longer day lengths in summer. Survival through winter months is the greatest challenge for such organisms. Wild plants have consequently developed diverse winter survival strategies (Sakai 2003). Overwintering domesticated plants such as winter cereals and forage crop have been selected and protected by humans, resulting in yield increases. Today, we are facing another difficulty, namely, global warming.
The infection process, sporulation and survival of Alternaria helianthi on sunflower
SUMMARY 
 
Electron microscopy was used to study the infection of sunflower leaves by Alternaria helianthi. Conidia germinated by producing one to many germ tubes which grew across the leaf surface before forming appressoria. The fungus directly penetrated its host through the cuticle and epidermis. Entry into the host through wounds and stomates was also observed. Extracellular sheaths were found to be associated with germ tubes and intercellular hyphae of A. helianthi. Conidiophores developed through collapsed stomates, from leaf veins, trichomes and also from mycelium growing across the host leaf surface. Microcylic conidia were produced directly from parent conidia under certain conditions. Studies using a volumetric spore trap showed that the airborne spore concentration followed a distinct periodicity with peaks occurring between 0900 and 1100 h each day. Laboratory studies showed that safflower, noogoora burr and bathurst burr could serve as alternative hosts for A. helianthi. The pathogen was readily isolated from sunflower crop debris from a diseased crop that had been harvested 1 yr earlier.