chromosome size, nuclear volume, and cellular volume ( Bennett, 1987 ; Grant, 1987 ), which has been called nucleotype effects ( Bennett, 1972 ). The nucleotype effects can cause variation in phenotypic traits such as seedmass, and many previous studies
Heritability of length of the reproductive period and rate of seed mass accumulation in beans (Phaseolus vulgaris L.) was estimated using 170 randomly derived F6 and F7 lines from three populations evaluated in the field in Puerto Rico and Honduras during two growing seasons. Narrow-sense heritability for length of reproductive period ranged from moderate (0.43) to high (0.83), and transgressive segregation for shorter and longer reproductive period was observed for the three populations. Heritability of rate of seed mass accumulation was low (0.24) to intermediate (0.49). Lines with high yield potential, which matured 4 to 7 days earlier than the later parents L227-1 and `Catrachita', were selected. Most of the superior lines combined earlier maturity with high yield potential by having greater rates of seed mass accumulation than the early parents `Cuarentena' and `Cuarenteño'. Low to intermediate heritabilities for rate of seed mass accumulation suggest that selection for this trait would be more effective by evaluating advanced generation lines in replicated trials. Several lines yielded significantly more than L227-1 or `Catrachita' by combining long reproductive period with fast rate of seed mass accumulation.
Open-pollinated southern highbush (V. corymbosum L. hybrids) and F1 (southern highbush × V. simulatum Small) hybrid blueberry seedlings were compared for fertility in a high-density nursery in Gainesville, Fla. Most of the pollen sources in the field were tetraploid southern highbush seedlings. Berries were collected from 100 southern highbush seedlings and from 100 seedlings from southern highbush × V. simulatum crosses. The seeds were extracted and dried on a laboratory bench for several days before weighing. No significant differences were found in seed mass/berry between the two types of seedlings. Although the F1 interspecific hybrids averaged slightly lower in seed mass per berry, this was due to the smaller size of their well-developed seeds, not to poor seed development. The estimated number of well-developed seeds per berry was 35.4 and 39.1 for southern highbush blueberries and their F1 hybrids with V. simulatum, respectively. These results indicate that reduced fertility should not be a problem in using V. simulatum to breed southern highbush blueberries.
To determine if multiple applications of GA3 would increase size of parthenocarpic fruit, and to assess the interaction between GA3 applications and pollination, `Beckyblue' rabbiteye blueberry (Vaccinium ashei Reade) flowers were treated with single or multiple applications of GA3 alone or in combination with full or partial pollination. Single or multiple applications of GA3 resulted in similar or increased fruit set compared with pollination, and increased fruit set compared with no pollination. GA3 applications decreased fruit mass and increased the fruit development period in comparison with pollination alone. Multiple, late applications of GA3 were ineffective in overcoming these effects. Partial (nonsaturating) pollination resulted in an average fruit set of 60%, while set following GA3 treatment in combination with full or partial pollination averaged 85%. Fruit mass was greater in the full pollination ±GA3 treatments than in all other treatments. The number of large seeds and seed mass per fruit were greatest in the full pollination treatment, and were significantly decreased by all treatments in which GA3 and/or partial pollination were used; however, there were no concomitant effects of GA3 in delaying the fruit development period. Our results indicate that under optimal pollination conditions, no detrimental effects of GA3 applications on fruit set, fruit size, or fruit development period in blueberry are to be expected, even though GA3 reduces seed number and seed mass. Furthermore, GA3 applications appear to be beneficial in increasing fruit set under suboptimal pollination conditions, although smaller fruit are to be expected under such conditions. Chemical name used: gibberellic acid (GA3).
function; sd, seasonal difference; SD, hourly temperature standard deviation; SM, seedmass; SRL, seedling root length. 1 Research agronomist. 2 Graduate student, Dept. of Plant Science and Mechanized Agriculture, California State Univ., Fresno, CA 93740
Institute Inc., Cary, NC). Dried seedmass as a percentage of total dried fruit mass (percent seedmass) and sugar concentrations were subjected to Box-Cox transformations to improve normality. Inspection of scatter plots of transformed compared with
An ovule passes through various contiguous phases during its development into a seed (Fig. 1). The first phase, histodifferentiation (or initial morphogenesis) (27), begins with fertilization and rapid cell division, leading to formation of the embryonic axis and of tissues that eventually accumulate reserve materials (3). Following this is the maturation or seed expansion phase, during which there is a marked increase in seed mass; cell expansion occurs as reserve deposition takes place. The 3rd and final phase, maturation drying (or desiccation), is characterized by a general reduction in metabolism as water is lost from the seed, which then passes into a quiescent, and sometimes dormant, state. This last phase is characteristic of temperate zone crops, but does not necessarily occur in tropical plants.
Maackia amurensis Rupr. & Maxim. associates with N2-fixing rhizobia, but variation in N2 fixation among genotypes of this species is not known. We determined the effect of N2 fixation on growth of plants from seven half-sib families known to differ in seed mass and seedling growth when provided N. Seedlings were grown in Leonard jars for 12 weeks in a greenhouse. Mass of control plants provided N and nodule mass on plants inoculated with rhizobia (USDA 4349) and not provided N differed among families. Among plants not provided N, inoculation did not increase dry matter but did reduce chlorosis. Therefore, plant N content also will be discussed as an indicator of efficiency of N2 fixation. Results indicate N2 fixation improves plant quality in low-N soils but will not eliminate the need for N applications during seedling production.
The fruit of several Opuntia species (prickly pear) are a good source of calcium, potassium, and ascorbic acid and are consumed fresh or processed as juices or preserves. Plants of Opuntia may be grown in arid and semiarid environments on marginal soils. Various cultivars, particularly in the species Opuntiaficus-indica, are grown commercially in the United States, Israel, Italy, Mexico, and South Africa. There is a need for new sources of genetic diversity and subsequent germplasm evaluation, and until recently, no publicly maintained germplasm collection of Opuntia existed in the United States. The purpose of this study was to evaluate fruit quality of 25 Opuntia accessions, originating from six countries, and maintained at the USDA collection at the National Arid Land Plant Genetic Resource Unit, Parlier, Calif. The largest fruits were harvested from plants of accessions PARL 201, 202, and 228 (227.6, 247.3, and 231.3 g/fruit, respectively). The hardest peel was on fruits of PARL 225 and 234 (both 3.7 kg), and fruit pulp of the same two accessions had the highest firmness (2.3 and 2.4 kg, respectively). Soluble solids in mature fruit varied from 6.1% (PARL 231) to 15.0% (PARL 254). The fruit color ranged from light yellow through orange, pink to dark purple. These characteristics and other traits such as fruit acidity, presence of spines, and seed mass/fruit indicated that the material represents a diverse germplasm collection, usable for future cultivar development.