Luca Languasco

Influence of Environmental Conditions on Infection of Peach Shoots by Taphrina deformans

ABSTRACT The effect of weather conditions on the infection of peach shoots by Taphrina deformans was investigated both under orchard conditions and in controlled-environment experiments. Leaf curl incidence and severity were related to rainfall, length of wet periods, and temperature during wetness and during the incubation period, as well as to the development stage of shoots. Surface wetness was more important than rainfall for infection to occur. Minimum rainfall for infection was 3 mm, with a wet period of at least 12.5 h; higher amounts of rainfall did not cause infection when the wet period they triggered was shorter. Wet periods initiated by dew or fog were too short for infection to occur. Infection occurred only when air temperature was <16 degrees C during the wet period and <19 degrees C during incubation. Logistic equations relating relative disease incidence and either duration of wetness or temperature were developed under controlled-environment conditions, with asymptotes at >/=48 h of wetness and </=8 degrees C for temperature, respectively. Rate of shoot and leaf development during the season influenced disease development, so that three different periods of susceptibility were defined, maximum susceptibility being between bud break and petal fall due to a low development rate of shoots.

Influence of Environmental Conditions on Spore Production and Budding in Taphrina deformans, the Causal Agent of Peach Leaf Curl

ABSTRACT Environment-controlled studies were carried out to determine the growth of Taphrina deformans under different conditions of temperature, humidity, and nutrient availability similar to those found on plant surfaces during the peach-growing season. Both ascospores and blastospores were able to bud at all temperatures tested (5 to 37 degrees C), with the optimum at 14 and 21 degrees C, respectively. Temperature <20 degrees C favored ascospore production and release, with the optimum at 10 degrees C. Budding was approximately two-and-a-half times higher in a film of water than on a dry substrate, with 100% relative humidity and blastospores also maintained a certain budding ability at lower humidity levels (minimum tested = 47%). Both spore types did not bud after approximately 50 to 55 h in the absence of external nutrients. In the presence of a periodically renewed carbon source, such as simple sugars, at concentrations that typically are present on peach plant surfaces, the fungus maintained its budding capability over time. Results showed that T. deformans is able to bud profusely under a wide range of environmental conditions that occur on peach tree surfaces. This work supports the hypothesis that T. deformans is a part of the normal epiphytic mycoflora of peach trees throughout the entire growing season.