065 Genetic Stability of Potato Leafroll Virus Coat Protein Gene in Transgenic Potatoes

Three potato (Solanum tuberosum L.) cultivars `Superior', `Irish Cobbler', and `Jopung' were transformed by co-cultivation with tuber discs and disarmed Agrobacterium tumefaciens LBA4404 carrying modified vector pBI121, that contained PLRV coat protein (CP) gene and controlled by CaMV35S promoter. Putative transformants were selected and their genomic DNA and RNA transcripts were analyzed for the confirmation of genetic stability by RT-PCR, PCR, southern, and northern blot. The growth characteristics and viral resistance of progenies of transgenic potato plants were investigated. Twelve lines among the different seven-times manipulated transgenic lines were grown in greenhouse and isolates trial field. PLRV coat protein gene was stably inherited in `Superior', but not in `Jopung'. `Jopung' was less stable than `Irish Cobbler' and `Superior' at genetic stability of PLRV CP gene. And some of these transgenic lines were highly resisted in PLRV multiplication. The yield of transformants was reduced in `Irish Cobbler' but not in `Superior'. Possible explanations for these types of resistance are gene silencing and positional effects of transformed PLRV CP genes and that had cultivar specificity. We consider the appearance of escaped transformants in `Jopung' for emergence of chimeric explants from early selection stage.

RESPONSE OF FOUR POTATO CULTIVARS TO METRIBUZIN TIME AND RATE OF APPLICATION

Over a 4-yr period (1974–1977) the effect of metribuzin at three rates and times of application was evaluated on four potato (Solanum tuberosum L.) cultivars commonly grown on Prince Edward Island. Metribuzin applied preemergence and early postemergence had no adverse effect on marketable and total yields of Irish Cobbler, Netted Gem, Kennebec, and Sebago cultivars. Delaying metribuzin application until late postemergence resulted in significantly reduced marketable yields of Irish Cobbler and Sebago but not Netted Gem and Kennebec when compared with preemergence and early postemergence treatment. Total yields with late postemergence treatment were significantly less than those with the preemergence treatment for all four cultivars and significantly less than early postemergence treatment with Irish Cobbler and Sebago.

REDUCTION IN DAMAGE TO POTATOES BY LEPTINOTARSA DECEMLINEATA (COLEOPTERA: CHRYSOMELIDAE) BY MIXTURES OF INSECTICIDES AND SILICA

The efficacy of insecticide–silica mixtures depended on brand of silica, i.e. Ar6gen®500, Hi-Sil®233, Micro-Cel®A, and Zeolex®100; number and population density of pest species; and cultivar of potato. In greenhouse tests, changes in the proportions of carbaryl and Arogen®500 in mixtures did not change efficacy; a 600 ppm carbaryl – 5400 ppm Arogen®500 mixture was as good as 1000 ppm carbaryl; and mixtures with either phosmet or pirimiphos-methyl and any silica with 30 ppm of insecticide and 270 ppm of silica were as good as 100 ppm of insecticide using mortality, repellency, and feeding rate as criteria. In the field at high density of L. decemlineata and low aphids, a 600 ppm carbaryl – 5400 ppm Arogen-500 mixture reduced larval populations by 66% and increased yield of Irish Cobbler 18-fold; and foliage treated with a 2000 ppm phosmet – 18,000 ppm Arogen-500 mixture was less attractive to adults than foliage treated with 2000 ppm of phosmet though the mixture was not superior to phosmet in effects on yield. At medium density of L. decemlineata and low aphids, a 500 ppm pirimiphos-methyl – 4500 ppm Zeolex-100 mixture increased yield of Irish Cobbler by about 100% and of Sebago by about 200% and a 600 ppm carbaryl – 5400 ppm Arogen-500 mixture was about 32% better than 1300 ppm carbaryl in effects on yield of Sebago. At low density of L. decemlineata and high density of aphids, 1000 ppm of carbaryl and various mixtures of carbaryl and Arogen-500 increased aphids by 109%, reduced coccinellid predators by one third, and reduced yield of Irish Cobbler and Sebago by 12%.

RELATIONSHIP OF CHIPPING QUALITY OF POTATOES TO MATURITY AND STORAGE TEMPERATURE

Acceptable chip quality based on chip color was obtained in five potato cultivars freshly harvested in August, September and October. Placing the tubers in 5 °C storage severely impaired chip quality. Reconditioning the tubers at 21 °C for 2 weeks improved chip quality in the cultivar Kennebec harvested in October and in two experimental cultivars, F5208 and F5889 harvested in September and October. Tubers of the cultivars Warba and Irish Cobbler from all harvests failed to become reconditioned satisfactorily. Preconditioning tubers at 21 °C before storing them at 5 °C and then reconditioning at 21 °C improved chip color in all cultivars. The color improved to an acceptable level in tubers of Kennebec harvested in October and of the experimental cultivars harvested in September and October. In these also, preconditioning produced good chip color when tubers were chipped directly from 5 °C storage. Tubers from all harvests of the experimental cultivar F5889, including those harvested when immature in August, chipped well from storage at 5 °C after 5 weeks of preconditioning at 21 °C.

VARIABILITY WITHIN ISOLATES OF VERTICILLIUM ALBO-ATRUM FROM POTATO

A monospore analysis of fresh isolates of Verticillium albo-atrum Reinke & Berthold from eight locations and six varieties of potato in Prince Edward Island, showed that, with one exception, the mass isolates were composed of morphologic forms distinguishable in growth habit and in capacity to form dark resting mycelium. One chief component, resembling the parent form, was present in all isolates. Pathogenicity trials in the greenhouse showed that the monospore forms differed in virulence and that virulence was not associated with the capacity to form dark, resting mycelium. Some monospore forms were avirulent, and one series was found that was equally pathogenic on both the highly susceptible variety Irish Cobbler and the field resistant variety Houma.

Comportamento de variedades de batatinha importadas do Canadá

No presente artigo são relatados os resultados de 14 experiências levadas a efeito em seis localidades do Estado de São Paulo, para estudar o comportamento das seguintes variedades de batatinha (Solanum tuberosum L.) importadas do Canadá: Katahdin, Green Mountain, Irish Cobbler, Pontiac, Keswich, Sebago, Kennebec, White Bliss e Canso. Tôdas são de polpa clara e, portanto, de menor procura pelo consumidor paulista. Em diversas partidas as batatas-semente eram excessivamente grandes para ser usadas inteiras, uma vez que a prática de dividir os tubérculos para o plantio não é recomendada para as nossas condições. As variedades experimentadas mostraram-se suscetíveis à pinta preta, causada pelo fungo Alternaria solani Kuhn, um dos problemas que mais interferem no bom êxito da cultura em nosso Estado. Green Mountain e Sebago foram as mais sensíveis à requeima devida a Phytophthora infestans (Mont.) de Bary. Green Mountain foi a mais produtiva, seguida de Katahdin, enquanto Irish Cobbler produziu melhor em terreno de baixada, rico em matéria orgânica e sob irrigação. Tôdas elas mostraram ser produtoras de tubérculos graúdos, especialmente Kennebec e Katahdin. O exame dos tubérculos colhidos evidenciou serem G. Mountain e Sebago sujeitas às manchas internas (chocolate), Kennebec, ao coração ôco, G. Mountain ao embonecamento e coração prêto, Katahdin e Canso, aos fendilhamentos. Tôdas as variedades estudadas mostraram-se, ainda, suscetíveis à formação de galhas ou pipocas devidas a nematóides - Meloidogyne incognita (Kofoid & White, 1941) - Chitwood, 1949.

MEASUREMENT OF CHIPPING QUALITIES IN MANITOBA-GROWN POTATOES

Of ten varieties of potatoes from three major producing areas of Manitoba, Cherokee, Irish Cobbler, Norland and Netted Gem each produced high quality chips in at least one area. Variations in chipping qualities occurred between localities. Reducing sugar and specific gravity were reliable indexes of chip quality. A simplified method for measuring chip colour is outlined.

SOME BIOCHEMICAL CHANGES ON STORAGE IN POTATOES FROM PRINCE EDWARD ISLAND, AND THEIR RELATION TO THE QUALITY OF CHIPS

Different varieties of potatoes were characterized by differences in their content of water, starch, and reducing sugar, and in susceptibility to change in response to the surrounding temperature.A critical concentration of 0.4 per cent reducing sugar was found, above which chips were dark brown, and unacceptable in flavour. Storage at 35° F. caused a rise in the concentration of reducing sugar in all varieties to between 1.5 and 4.0 per cent in 5 to 14 weeks. During storage at 50° F. the reducing sugar usually rose above 0.4 per cent in 9 to 13 weeks.Shrinkage and rot developed markedly in the Sebago, and to a less extent in the Katahdin, when the temperature was raised from 50° or 35° to 70° F., and the chips produced from them were poor in texture and flavour.A fall in the level of reducing sugar below 0.4 per cent occurred in 3 to 9 weeks during conditioning at 70° F. in the Netted Gem, Green Mountain, and Irish Cobbler varieties, and the chips from these were acceptable.The biochemical behaviour of the Netted Gem and Irish Cobbler was most conducive to the production of acceptable chips.