Chlorogonoplasty ID nasionach i bulwach ziemniaka – Solarium tuberosum L. jako wskaźnik odporności na streptomykozy [The chlorogonoplasts in the seeds and tubers of potato – Solatium tuberosum L. as indicator of resistance to the streptomycosis]

Few varieties of <i>Solanum tuberosum</i> L. were investigated by histochemical methods. The dependence between the presence of the chlorogonoplasts and the resistance of the tested varieties to streptomycosis was found.

ELECTROPHORETIC DETECTION OF PARASITISM BY DRYINIDAE IN TYPHLOCYBINAE LEAFHOPPERS (HOMOPTERA: AUCHENORRHYNCHA)

Nine species of the subfamily Typhlocybinae (Auchenorrhyncha: Cicadellidae) were collected from Corylus avellana L., Solatium tuberosum L., and Vitis vinifera L. Seven species were parasitized by Dryinidae, among which Alebra coryli Le Quesne 1977 and Edwardsiana staminata (Ribaut, 1931) were recognized for the first time. Clearly parasitized and apparently unparasitized leafhoppers and dissected dryinid larvae were assayed by polyacrylamide gel electrophoresis. The α-glycerophosphate dehydrogenase (α-GPD) enzyme system proved to be a reliable tool for indicating the presence of dryinids in all sampled species: the parasitized adults always showed a fast band, which was absent in unparasitized adults. The α-GPD was a reliable enzyme system to detect dryinids at an early stage of their development but not to discriminate among dryinid species. The occurrence of dryinids in the males of A. coryli and Zygina rhamni Ferrari, 1882 was also pointed out by the change of their colouration.

Occurrence of common scab in potato tubers after foliar treatment with glycinebetaine under glasshouse conditions

A single foliar spray with 2.5 mM glycinebetaine (GB) was applied on potato (Solatium tuberosum L.) cvs. Matilda, Sabina and Saturna grown in a sand bed infested with Streplomyces scabies (Thaxter) Waksman & Henrici at tuber initiation. A period of drought was maintained after GB treatment to enhance scab infection. Logit models were used to compare scab incidence in all harvested tubers (n = 622) and the type of scab in the symptomatic tubers (n = 382), whereas the tuber surface areas covered with scab lesions were compared using ANOVA. A 10 g increase in tuber weight increased the odds of scab incidence by 11.3%. Scab incidence was lowest in Sabina and highest in Matilda. Raised scab and superficial scab were common in all cultivars, but pitted scab developed only in a few tubers of Sabina and Matilda. Among the scabby tubers, the incidence of raised scab was highest in Sabina and lowest in Saturna. The mean surface area covered with scab was 32.8% in Matilda, 11.7% in Saturna and 7.5% in Sabina. Treatment with GB slightly reduced the severity of scab symptoms, as shown by the reduction in the proportion of tubers with raised scab among the scabby tubers (odds 0.60). No effect on the incidence of scab or the tuber area covered with scab lesions was detected following GB treatment.

Effect of the developmental stage of potato seedlings on recovery after transplanting to the field and on tuber yield

SUMMARYUnder the short-day conditions and cool temperatures prevailing from January to March in the Nile delta, Egypt, potato (Solatium tuberosum) seedlings grown from true potato seed formed tubers in the nursery when the plants were less than 5 cm in height. In order to examine the hypothesis that slow field establishment after transplanting and low tuber yields of these seedlings were caused by premature tuberization, different treatments to delay tuberization were applied in the nursery before transplanting.Increasing the air and soil temperature in the nursery accelerated both the development of the above-ground and below-ground shoot organs, but did not improve field establishment of the seedlings after transplanting. Extension of the photoperiod with incandescent dim light, exogenous application of gibberellic acid (GA), and removal of the shoot apex to encourage the growth of lateral branches from the leaf buds increased biomass allocation to the above-ground shoot organs, decreased tuberization in the nursery and accelerated field establishment of transplanted seedlings. Extension of the photoperiod was the most effective treatment to delay tuberization, and doubled the final tuber yield from transplanted seedlings.The results are in agreement with the hypothesis that poor field establishment and low final tuber yields from potato transplants may be caused by the presence of strong tuber sinks at transplanting, which reduce assimilate partitioning towards the roots and above-ground shoots.