In each of seven field experiments, density of watermelon (cultivar Sugar Baby) plants was varied over the range 1000-9000 plants/ha by varying the distance between plants in single-row, replicate plots. Per unit area, reproductive biomass and marketable yield each increased linearly with density. An upper limit on these response variables at high density was not detected in any experiment. The rate of increase per 1000 plants/ha ranged from 1.1 to 3.2 Mg·ha-1, for reproductive biomass, and from 0.5 to 1.1 Mg·ha-1, for marketable yield. The linear effect of density explained >90% of the increase in reproductive biomass in most experiments. The effect on marketable yield was more variable because the marketable fraction of reproductive biomass often was highly variable. In most experiments, the marketable fraction did not vary systematically with density. The linear rate of change in the marketable fraction with density did not exceed 3% per 1000 plants/ha on average in any experiment. Intraspecific competition intensified rapidly as density was increased in some experiments. Intensity of competition appeared to vary among environments.
James A. Duthie, James Shrefler, Warren Roberts and Jonathan V. Edelson
Ray A. Allen and Curt R. Rom
Light distribution in two cultivars on three dwarfing rootstocks in three high-density apple tree training systems was measured in the sixth leaf beginning at full bloom and continuing through the season. Training system had a significant effect on light penetration into the lowest point of the canopy (measured at 0.5 m), with the slender spindle being significantly darker than either the central leader or the vertical axis, although all three systems were below the threshold value of 30% full sun (FS) needed to maintain productivity for most of the season. Cultivar had no significant effect; however, trees of both `Jonagold' and `Empire' fell below 20% FS early in the season and remained there until late in the season. Rootstock had the greatest effect, with trees on M9 and M26 being significantly darker in the lower canopy than trees on Mark. Trees on M26 and M9 fell below 10% FS early in the season and remained there, while trees on Mark never fell below 20% FS.
Aurora Díaz, Antonio Martín, Pilar Rallo, Diego Barranco and Raúl De la Rosa
We studied the self-incompatibility of two main Spanish olive (Olea europaea L.) cultivars, `Picual' and `Arbequina', by testing the selfing of the seeds with microsatellites. For this purpose, we used a rapid single-seed DNA extraction method and four highly polymorphic microsatellites. We analyzed seeds produced in branches bagged for selfing from mono- and multi-cultivar orchards in 2002 and 2003. We did not find any seed coming from selfing in the bagged branches, for either cultivar, in the two types of orchards. Additionally, we tested seeds coming from free pollination in mono-cultivar orchards from different locations. In the case of `Picual' olive, only three seeds out of the 70 collected were the product of selfing, although they came from mono-cultivar orchards located in areas where the cultivar used as the female parent was predominant. From the 20 seeds of `Arbequina' olive harvested in the middle of two high-density plantations, not one was a product of selfing. According to this, olive would behave as an allogamous species in mono-cultivar growing conditions and the pollen coming from long distances would be able to produce a normal bearing. Therefore, there is strong evidence to support the idea that the cultivars studied could be self-incompatible. Future experiments in self-compatibility should include a paternity check of the possible self seeds obtained.
Elhadi M. Yahia
Grapes (Vitis vinifera L. cv. Thompson Seedless) were packed in low density (LDPE) and high density (HDPE) polyethylene bags (Bag size: 25×25 cm containing 300 g of fruit). LDPE and HDPE films had a thickness of 38.7 and 28.2 μm, water permeability of 960 and 720 g/m2.hr.atm., and O2 permeability of 7030 and 3700 cc/m2.day.atm., respectively. Carbon dioxide gas (400 cc) was introduced to the bag immediately after sealing, after 2 weeks. and/or after 4 weeks. Fruits were evaluated after 3 months at 0°C. CO2 was about 30% immediately after introducing the gas but its concentration was reduced to less than 1% within 3 to 4 days. O2 was maintained very high (higher than 10%) in all packages. Water loss and shriveling were very low. However, decay incidence was high in all packages. In-package atmospheric conditions were not appropriate in all treatments to suppress decay activities. Further studies will be carried out with films less permeable to atmospheric gases, and fruits will be evaluated after shorter storage periods.
Owusu Bandele, Xenia Wolff, Byron Belvitt and Justin Egbe
Two experiments were conducted in 1988 and 1990 to determine the effects of planting density, N fertilizer rate, and cultivar on fresh yield of dill. A split plot design was used in the first experiment in which planting density (one versus two rows per bed) was the main plot treatment and N rate (0, 56, 112 kg/ha) was the subplot treatment. A European cultivar, `Crown,' was used in the first experiment in 1988 while `Long Island Mammoth' was planted in 1990, N was applied in split applications while both K2 O and P2 O5 were preplant incorporated at the rate of 134 kg/ha. Planting was done on bedded rows approximately 66 cm wide and 15 cm high. N fertilizer application did not affect yield in 1988. Leaf, stem, flower, and total yields were greater for the high density planting. The second experiment evaluated yield of four cultivars (`Tetra,' `Bouquet.' `Long Island Mammoth,' and `Crown') using a randomized complete block design. `Long Island Mammoth' and `Tetra' produced greater leaf and total fresh weight while `Long Island Mammoth' and `Bouquet' produced greater flower fresh weight.
W.R. Okie, T. G. Beckman and A.P. Nyczepir
Lovell rootstock is recommended for Peach Tree Short Life (PTSL) sites in the Southeast because it outlives Nemaguard. No genetic studies of PTSL tolerance have been done. Clonally replicated peach seedlings [Prunus persica (L.) Batsch] of Lovell, Nemaguard and four F1 selections of Lovell × Nemared were tested for field survival in a high density planting on a PTSL site. Rootstock families (12 seedlings × 8 ramets each) differed in growth, survival and longevity. Genetic variation was comparable to environmental variation for most families. Based on seedling within rootstock family, estimated broad-sense heritabilities for survival and longevity were high. The use of clonally replicated seedlings allowed the selection of apparently superior individuals from both Lovell and the other more short-lived rootstock families in a single screening after 6 years. Survival of Lovell at that time was 50% compared to 16-29% for other families. Across all families, all 8 ramets were dead for 21 seedlings, whereas all 8 were alive for only 3 seedlings.
Jack Jordan, E.J. Gregory, D. Smith and I. Benally
A three density-three rootstock test was conducted on three spur-type apple cultivars grown in sandy loam soil. Trees of the three cultivars: `Redspuree' (RS), `Goldspuree' (GS), and `Spuree Rome' (SR) were trained to a central leader system in a 100% grass cover. All cultivars produced best in the high density planting (1344 trees/ha.). Most consistently and significantly affected were the SR. The least productive density, the low density, had 336 trees per ha. while the medium density had 672 trees/ha. Density had a more significant effect on SR culls and a slightly more significant effect on SR fruit soluble solids than it did on these variables of the other cultivars. Density had little effect on fruit firmness of all cultivars. Of these rootstocks: m7a, m26, and mml06, the mml06 rootstock usually produced the greatest yields, especially in the RS and SR cultivars. Results for the GS were more variable than they were for RS and SR with its production on the m7a rootstock occasionally exceeding that of the mml06 rootstock. The m26 rootstock produced the lowest yields. Rootstock had no significant effect on fruit firmness of all cultivars.
Zhenhua Guo and John C. Snyder
Choice and non-choice bioassays were used to examine deterrence in vitro and in vivo of Tetranychus urticae Koch. In vivo deterrence of leaflets from 11 Lycopersicon hirsutum accessions as well as the tomato cultivar `Ace 55' was measured as was in vitro deterrence of their leaf hexane extracts. Leaf surface chemistry was examined by gas chromatography. All 6 accessions of L. hirsutum f. hirsutum contained sesquiterpene hydrocarbons. Each of these extracts also contained one or a few late eluting components. All were deterrent in vitro and 5 out of the 6 were deterrent in vivo. The one lacking in vivo deterrence had low density of type IV trichomes. All 5 accessions of L. hirsutum f. glabratum contained methyl ketones. These accessions were less deterrent in vitro and 4 out of the 5, less deterrent in vivo. The one accession having high in vivo deterrence also had high density of type IV trichomes. `Ace 55', having few hexane extractable compounds was neither deterrent in vitro nor in vivo. Within an accession, secretions from different types of trichomes shared similar chemical profiles and were similar to leaf profiles.
Joseph A. Fiola
High density strawberry planting systems have increased yield and fruit quality, and allow greater production on small acreage. To adapt the system to New Jersey conditions, replicated plantings of `Chandler', `Tribute', and `Tristar' were established at 3 spacings and two planting dates (9/9, 9/15) in 1989, and two plant spacings and two planting dates (8/14, 9/7) in 1990. Plants were propagated as plugs from runner tips. The plantings were covered with floating row covers (polypropylene) in December, covers were removed in early April at 5% bloom. In 1990, `Chandler' yield increased as density increased, and decreased with later planting date. Fruit quality was very good; saleable % was over 90%. Size ranged from 8 to 21 g., and averaged from 12 to 17 g. for the various treatments. `Tribute' responded similar to `Chandler' but `Tristar' yield at 12″ was not significantly different than 6″, but greater than 9″. Size ranged from 9 to 19 g., and averaged from 10 to 14 g.; saleable % was over 85%. In 1991, 2 spacings (6″, 12″) and 2 planting dates (8/24, 9/7) were tested. The earlier planting date was superior to later; yields were not different between the 6″ and 12″ treatments (yield range: 3.8-5.4 T/A). Size was superior at wider spacing; day-neutral fruit size was small (avg fruit size range: 7.7-11.2g; high range: 10.1-17.4g).
Watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] cultivars StarBrite and Crimson Sweet were grown during 1991 and 1992 in rows 1.5 m apart at plant spacings of 0.9, 1.5, or 2.2 m. Total fruit yield, marketable fruit yield, fruit-weight distribution, and estimated gross returns were determined for each spacing treatment. Total and marketable fruit yields were greater overall for `StarBrite' than for `Crimson Sweet'. Except for 1991 `Crimson Sweet' yields, marketable fruit yields per unit land area increased 29% to 34% as plant spacing decreased from 2.2 to 0.9 m. The yield component contributing the most to increased yields with high-density plantings was increased fruit count per unit land area. Average fruit weight responded only slightly to decreased plant spacing. Fruit-weight distribution on a relative frequency scale was stable regardless of plant spacing or production year. The potential for increasing gross returns per unit land area exists by increasing watermelon plant populations beyond the current Georgia recommendation of 2500 to 3000 plants/ha.