Nitrogen fertilizatioin of potatoes for early summer harvest

Rates of N applied to sandy loam soil with wheat as the preceding years crop was studied as to the influence on tuber yields of potatoes grown for early summer harvest in Southwestern Indiana. Most of the yield response was to the first 75 lbs/acre (84 kg/ha) increment of N which increased the yield of US #1 potatoes 61 cwt/acre in 1967 and 52 cwt/acre in 1968. The total solids were not significantly decreased by the first increment of N applied which was also the N range of rapid yield increase. N fertilization increased the N content of the foliage from 3.0 to 4.0% in 1967 and 3.97 to 5.17 in 1968 and the tubers from 1.36 to 2.96 in 1968. The first 75 lbs N increment was efficiently converted to crude protein, 48% incorporation, but the succeeding increments were poorly converted.     

Screening potatoes for field resistance to early blight

A satisfactory method has been developed for screening potato clones for field resistance to early ligbht. Differences in clonal resistance can be evaluated and have proven to be consistent. Resistance to foliar infection appears to be generally associated with plant maturity. Late maturing selections are generally quite resistant and early maturing selections are usually extremely susceptible. Differences in resistance among named varieties from throughout the world were extremely variable.     

The effect of green sprouting on yield of early potatoes

Three yield trials of early sizing potato seedlings and varieties were conducted at separate locations over a two-year period in New Brunswick, Canada. Two preplanting treatments of the seed were used: green sprouting for 3 weeks at 65 F (18 C) and check samples from storage at 45 F (7 C). Graded yield results and specific gravity determinations obtained 82 days after planting are presented. A highly significant increase (16–28%) in yield of marketable tubers was obtained from the green sprouted treatments. Higher specific gravities were recorded for 32 of the 43 green sprouted plots over the checks.     

Patterns of stem water potential in field grown potatoes using stem psychrometers

Summary The first large scale outdoor measurements of potato (Solanum tuberosum L.) stem water potential (SWP) usingin situ temperature-corrected stem psychrometers were performed on three cultivars common to Ontario, Canada (Atlantic, Monona and Norchip). Potato plants were examined under three soil water treatments which included rainfed, irrigated and stressed through the use of rain shelters. Cultivar variations in SWP under both irrigated and rainfed conditions were slight (P>0.05), although some significant (P<0.05) differences in mid-day SWP were evident, especially under conditions conducive to high atmospheric water demand. Under these conditions. cv. Atlantic maintained the lowest SWP with cv. Monona highest and cv. Norchip was intermediate. Few differences in pre-dawn SWP were detected between the three cultivars under well watered and rainfed conditions. Under low soil water, significant differences (P<0.05) were observed. The similar trend of Atlantic maintaining the lowest SWP with Monona the highest was consistent.     

Disease assessment of early blight in potatoes in semi-arid zones

Summary Five methods of assessing early blight (Alternaria solani) on potatoes were examined using field trials in Israel in 1986 and 1987. One method (Mean Days) was unrepeatable and therefore unsatisfactory; four others were repeatable and discriminated between the 16 cultivars examined. However, when relationships with natural senescence were examined, two of the methods (Best Score and Mean Percent) were highly correlated with it. Of the two methods that reflected the rate of increase in disease symptoms, the maximum increase in percentage cover observed in a 14 day period (Delta) was found to be more effective than the linear regression coefficient for the relationship between percentage disease cover and number of days from planting (Slope).     

Pre and early post-emergence weed control with Paraquat in potatoes

Studies using Paraquat herbicide for early post-emergence control of broadleaved and grass weeds in Katahdin and Russet Burbank potatoes were conducted in Maine during four growing seasons. All rates and times of application of Paraquat gave good commercial control of grass and broadleaf weeds when compared to Premerge and Dowpon treatment as checks. Paraquat applied to Katahdins 2 weeks after ground crack reduced the yield of tubers but did not significantly affect specific gravity. Yield and specific gravity of Russet Burbank was reduced by Paraquat applied one and 2 weeks after ground crack. Paraquat can be used effectively for weed control in Katahdin up to one week after ground crack without crop damage. In Russet Burbank it appeared that application at ground crack was about as late as Paraquat could be applied without affecting yield or specific gravity of tubers.     

Interrelations between nitrogen and phosphorus fertilization and early blight control of potatoes

Three different rates of soil-applied nitrogen were combined in all possible combinations with different schedules of fungicidal sprays for early blight (Alternaria solani) control in field experiments for three consecutive years. The nitrogen was applied with a constant rate of phosphorus. Yield response to fungicidal sprays was more pronounced when potato plants had received nitrogen and phosphorus. Both spraying and fertilizer application reduced the percentage of leaflets infected by early blight. However, the effect of the fungicide was greater than that of fertilizers. Estimates based on the cost and price assumptions indicated that $1.00 investment in the optimum number of fungicidal sprays at the adequate rate of fertilizer returned $8.34, $9.71 and $1.89 in 1970, 1971 and 1972, respectively.     

Life strategies and spatial arrangement of grasses in a Mediterranean ecosystem in Greece

The temporal and spatial distribution, and the life strategies, of fifteen grass species in a Mediterranean evergreen sclerophyllous formation at Petralona (Chalkidiki, Greece) were studied in order to identify the relationships between species, and among species and the environment, which allows for the coexistence of species. The grass species were grouped into (i) early annual species that were characterized by early germination and a relatively long growth period; they did not need excessive resources and were distributed over the entire site, (ii) late annuals that were characterized by late germination and a short growth period; they required resources within this limited period and were competitive in capturing them and so were confined to the most productive sites of the site and (iii) perennial grasses that were characterized by early germination and vegetative reproduction; they were tolerant to nutrient shortages and hence maintained their distribution on the site. The spatial arrangement of species can be considered as a response to the selective pressures of the seasonal water and resource availability in a Mediterranean environment. This environment posed temporal limitations on the activity of early annual and late annual species, which restricts them in time and space. The perennial species overcame this by being flexible in their resource capture and use, because of their ability to store nutrients.     

Effects of differential rates of nitrogen and phosphorus on early blight in potatoes

The Kennebec variety of potato was exposed toAlternana solani inoculum during the 1970 and 1971 seasons to determine the effects of differential rates of nitrogen and phosphorus on the incidence of early blight. Both high nitrogen and low phosphorus treatments significantly reduced the incidence of early blight and the combination of high nitrogen and low phosphorus consistently gave the lowest incidence of the disease during both years. The data suggest that this combination of nutrients may be related to early blight resistance in the plant by extending the period of meristematic activity permitting the plant to wall off infection. Yield data indicated that there was too great a yield difference between fertilization for optimum early blight control and fertilization for optimum yield. Therefore, in Maine, potatoes should be fertilized for optimum yield with a reasonable specific gravity, and early blight should be controlled by the application of fungicides and sanitation measures.     

Growth of early potatoes from different portions of seed tubers II. Yield

Several of the recently released early-potato (Solanum tuberosum L.) cultivars used in Ontario have produced uneven stands which have been shown to be a result of delayed emergence from basal end seed pieces. A study was conducted to evaluate the effects of seed portions on the yield of three early potato cultivars, Jemseg, Superior and Yukon Gold. Yield of plants from basal seed pieces was lower than that from apical seed pieces or whole tubers for Jemseg and Yukon Gold during several sequential harvests. With Superior, cut seed portions yielded less than whole seed. Number of stems per plant was lower for basal plants of Jemseg. Tubers with strong apical dominance or dormancy such as Jemseg and Yukon Gold are prone to differences in yield among seed portions.     

Screening for field resistance to early blight (Alternaria solani) in potatoes

Summary 27 clones were trialled in the Negev, Israel, in the Spring and Autumn seasons of 1984 and 1985, in a control area (kept disease free) and an Alternaria area (artificially infected withA. solani). Disease symptoms and maturities were assessed. Significant variation in symptom expression was detected between clones and seasons, as well as a significant interaction of clones by years by seasons. The symptoms showed low correlations between seasons but were larger between years within the same season. The clones displayed a range of maturity scores and it was demonstrated that these showed a relationship with the variation in observed disease symptoms. The deviation of symptom expression from a linear relation with maturity was taken to reflect a clone's actual resistance or susceptibility. The results showed agreement over years and it was suggested that such trials and methods of assessment might provide the basis for screening large numbers of clones.     

The response of cassava (Manihot esculenta) to spatial arrangement and to soybean intercrop

Response of cassava to row spacing and plant population density (0.62 plants m⁻² in 180-cm rows; 1.23 plants m⁻² in 90-, 180-, 270-, and 270- plus 90-cm (i.e. paired rows); and 2.46 plants m⁻² in 90- and 180-cm rows), and to soybean intercrop at two row spacings of cassava (90 and 270 cm) was studied at a high latitude (27°S) in south-east Queensland, Australia, where low temperature limits a growing season to 9 months. Detailed observations were made in sole crops on leaf canopy structure and light penetration in the three row spacings at the medium density to allow an estimation of light availability for an intercrop between cassava rows.The low plant density or the 270-cm row plants produced the lowest total dry matter and tuber yield at harvest, while the two higher densities or the two narrower rows produced similar total and tuber dry weight. Intercropped cassava produced a similar tuber yield to the sole crop at the corresponding spatial arrangement, but total dry matter was lower in the former.Leaf area index was similar among the 90-, 180- and 270-cm row spacings in sole crops throughout the growth period. However, leaf area was unevenly distributed horizontally for a longer time as row spacing increased. This resulted in light penetrating the inter-row space for a longer period in wider rows in sole crops, more than 50% full sunlight reaching soil level for 90, 120 and 130 days after planting in the 90-, 180- and 270-cm rows, respectively. This light environment would be available for an intercrop if cassava growth is not affected by the intercrop. The results for cassava intercropped with soybean show that in fact cassava growth was reduced by the associated soybean, and hence light available for the soybean growth would have been more than that estimated above.     

马铃薯转基因研究进展

简要介绍马铃薯转基因技术方法,着重对已获得的转抗真菌病基因、抗病毒基因、抗虫基因、改良品质基因的马铃薯的特征特性,以及将马铃薯作为植物生物反应器来生产有用蛋白质和疫苗等方面的研究成果进行了综述,同时还对转基因马铃薯的生物安全性作了评价和展望。