Potato Stems Research Articles

Survival ofPhytophthora infestansin Potato Stem Lesions at High Temperatures and Implications for Disease Forecasting

KABLE, P. F., and D. R. MacKENZIE. 1980. Survival of Phytophthora infestans in potato stem lesions at high temperatures and implications for disease forecasting. Plant Disease 64:165-167. The ability of Phytophthora infestans to produce sporangia in 7-day-old lesions in potato stems after exposure to constant temperatures of 30-40 C was examined. Constant 30 C temperature had no effect, but 32.5 C was lethal to some sporangia, and the rate of mortality increased with higher temperatures. The relationship between diminished survival and duration of temperature exposure was found, by regression analysis, to be best expressed by a negative exponent over time and varying with temperature. However, survival at 40 C appeared to decline linearly with time. These data indicate that the provision of BLITECAST (a computerized late blight forecasting system) that cancels infection periods when temperatures the following day are 30 C or above may need modification if the system is used in hot climates.

Persistence ofCorynebacterium sepedonicum in soil and in buried potato stems

The effect of moisture content and temperature on the persistence, in soil, of cells of the ring rot bacterium,Corynebacterium sepedonicum (Spieck. and Kotth.) Skapt. and Burkh., was followed with root-inoculated, rooted potato stem cuttings. Ring rot bacteria were still viable after 284 days in a sterilized Lethbridge silt loam moistened to field capacity and incubated at 15°C. However, the cells did not survive beyond 6 days in two non-sterile silt loams at field capacity and 20°C. In non-sterile Lethbridge silt loam, persistence of the pathogen increased as soil moisture content and temperature decreased. Cells persisted for 10 and 15 days, respectively, in soil at 50% field capacity held at 15 and 10°C. Ring rot bacteria were not recovered after 88 days from a non-sterile Lethbridge silt loam moistened to the wilting point and held at a temperature fluctuating between 10 and 20°C, or from soil at field capacity and at a temperature fluctuating between −5 and +5°C. They survived for 362 days in soil at the wilting point at mean temperatures of 0 or −10°C, but were not viable after 278 days in soil at field capacity and a mean temperature of −10°C. In excised, infected potato stems held in a non-sterile Lethbridge silt loam, the pathogen persisted for 325 days in soil at the wilting point and a mean temperature of 0°C. These results suggest that soil infested with ring rot bacteria should be kept well moistened during warm periods to inactivate these bacteria and to ensure that they do not contaminate healthy tubers that may be stored or grown there later.

Anatomical Response of Potato Stems and Roots to Soil Moisture and Rates of Fertilizer1

AbstractThis study was conducted to determine the effect of three moisture regimes and three rates of fertilizer on the anatomy of stems and roots of the ‘Katahdin’ cultivar of potato, Solanum tuberosum. A Caribou loam (coarse loamy, mixed frigid Dystric Eutrochrept) was used in a greenhouse experiment. The soil was placed in pots. Fertilizer at rates of 0, 168, and 336 kg N/ha, in a 10‐15‐15 mixture, was used. Soil moisture stresses equivalent to 3C, 50, and 70% depletions of available moisture were allowed to develop. The data showed that the area of the xylem in the stems decreased as soil moisture stress increased. The highest rate of fertilizer reduced the area of the xylem, but increased the diameter of the individual vessels. In the roots the area of xylem and phloem decreased while the area of cortex increased with an increase of soil moisture stress in the 75‐day experiment. The area of xylem tended to increase while the cortical tissue tended to decrease with increases in the rate of fertilization.

Recurrence of soft rot coliform bacterial infections in potato stem cuttings: an epidemiological study on the central nuclear stock production farm in Scotland 1967–74

Propagation of potato stocks from stem cuttings has produced material almost entirely free from infection withErwinia carotovora var.carotovora andE. carotovora var.atroseptica: during 1967–74, very few infected plants or tubers were found on the nuclear stock farm. When infection occurred,E. carotovora var.carotovora was the organism most often isolated, whereas in ordinary commercial stocksE. cartotovora var.atroseptica predominates. In 1973 and 1974 dipterous insects caught at a nearby dump of decomposing vegetable matter were contaminated withE. carotovora var.carotovora several weeks before infection was found on potato stems. Serotypes ofE. carotovora var.carotovora isolated from insects and infected plants were very often identical, providing compelling evidence that the source of the organisms was the dump, from which contaminated insects dispersed and subsequently transferred organisms to the crop. The origin of infections withE. carotovora var.atroseptica remains unknown.

Ultrastructure of Potato Stems Infected with Corynebacterium sepedonicum

Ultrastructure of Potato Stems Infected with Corynebacterium sepedonicum