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Chun-Qing Sun, Zhi-Hu Ma, Guo-Sheng Sun, Zhong-Liang Dai, Nian-jun Teng and Yue-Ping Pan

to pollen quality, pollen germination, or embryo abortion. Pollen quality, pistil receptivity, and embryo and endosperm development have been widely examined in many crops, for example, Dendranthema grandiflorum , Nelumbo nucifera , Phaseolus

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Chunqing Sun, Zhihu Ma, Zhenchao Zhang, Guosheng Sun and Zhongliang Dai

barriers in this process can result in the failure of hybridization. These barriers are divided into pre- and postfertilization barriers, often described as stigma–pollen incompatibility and embryo abortion, respectively ( Deng et al., 2010 , 2017 ; Lee

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Michele R. Warmund and J.W. Van Sambeek

seedless citrus fruits and molecular approaches have been used to induce embryo abortion for seedless fruits in several other horticultural crops ( Callahan et al., 2011 ; Chavez and Chaparro, 2011 ; Lora et al., 2011 ). In our study, the presence of

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Chunxian Chen, William R. Okie and Thomas G. Beckman

fruitlet drop was primarily due to a freezing injury to the entire fruitlet, including skin, flesh, pit, and embryo tissue ( Rieger et al., 1991 ). A button or normally sized skin-damaged fruit could develop if frost damage caused only embryo abortion or

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Daniele Bassi and K. Ryugo

To learn why embryos of early ripening stone fruits abort or fail to germinate, the growth and nutrition of developing seeds of `Independence' nectarine and `Fay Elberta' peach (Prunus persica, Batsch.) were compared. Seeds were collected at weekly intervals, beginning 2 months after full bloom until the fruits were ripe. Fruit diameter, seed and embryo lengths, and fresh weights of nucellus and endosperm were recorded. Parts of the seeds were analyzed for soluble carbohydrates, fats, and total N. At the same phonological stages of fruit development, concentrations of these seed fractions were nearly equal for both cultivars. Percentage composition of all fractions varied with time, but increased on a per-seed basis. Sucrose was the major soluble carbohydrate in embryos of both cultivars. Nitrogen content of the embryos, on a percent dry matter basis, gradually decreased from the 12th week after full bloom to harvest.

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Aliza Vardi, Ilan Levin and Nir Carmi

pollination and fertilization occur and embryo abortion is the cause of seedlessness. Fruit development and seed set in flowering plants normally occur in a coordinated manner, after pollination of the stigma and a subsequent double fertilization event in

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M.K. Ehlenfeldt and M.R. Hall

T 286, a rabbiteye blueberry selection from a `Delite' × `Tifblue' cross, generally has been regarded as producing semi-seedless fruit. A comparison of nonpollinated flowers of T 286, `Delite', and `Tifblue' showed no differences in ovule count, and comparisons of ovules at 10, 20, and 40 days from manual cross-pollination showed no obvious evidence of embryo abortion. Manually cross-pollinated flowers contained 85, 60, and 38 seeds per fruit for `Delite', `Tifblue', and T 286, respectively. Open-pollinated fruit of T 286 had a seed count similar to that of open-pollinated `Tifblue' but possessed significantly heavier fruit. The number of seed in T 286 and `Tifblue' indicates a tendency toward parthenocarpy.

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Joseph H. Connell, K. Uriu, W. Micke and J. Uyemoto

Boron(B) deficiency in almond (Prunus dulcis Mill.) is characterized by leaf tip scorch, leaf drop, twig dieback, brown gummy areas in the endocarp, and embryo abortion followed by nut drop in May. Additional symptoms revealed by our work include failure of flowers to set nuts and lateral bud drop. Lack of production in part or in all of the free canopy causes spurs to elongate leading to a “willow twig” symptom on the small fruitwood. This can be confused with the nonproductive “bull” syndrome or with virus bud failure (ABFV or PRSV). Comparative leaf, pericarp, or kernel analysis in May gave a better indication of low B than did leaf analysis in August. In August, analyzing the hulls (mesocarp and exocarp) gave better separation between deficient and adequate trees than did leaf, kernel, or shell analysis. B critical levels for almond leaves should be re-evaluated since deficiency symptoms occur at currently accepted “adequate” levels.

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Lu Zhang, Robert Howard Beede, Gary Banuelos, Christopher M. Wallis and Louise Ferguson

Springtime flail mowing of row middles for weed control in California pistachio (Pistacia vera L.) orchards blows dust into the leafless canopy if it occurs during bloom. The effect of dust on pistachio pollination and fruit set is unknown. Rachises were bagged prebloom and hand pollinated with pollen and dust mixtures at 1:0, 1:1, 1:4, 1:16, and 0:1 volume/volume ratios on five successive days. The 2016 and 2017 trials demonstrated that the inflorescences treated with a high pollen:dust ratio (0:1, 1:4, and 1:16) had significantly lower split nut rates (commercially less profitable) compared with low dust ratio tests (1:0 and 1:1). Our results also showed that dust damaged both pollen viability and stigma quality, particularly if contaminated with herbicide residues (GlyStar® Plus and Treevix®). Decreased yield was a function of decreased fruit set; increased embryo abortion, parthenocarpy, or both; and a lower split nut percentage. The GA3 content in flowers of both the pollen and dust treatments was significantly higher than that in nonpollinated flowers, suggesting dust stimulated parthenocarpy, resulting in empty nutshells, “blanks” at harvest.

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Darren Touchell, Zenaida Viloria and Thomas Ranney

Weigela Thunb. consists of 12 species distributed throughout Northeast Asia. Diervilla Mill. is a closely related genus containing three species endemic to North America. Taxa from both of these genera are important nursery crops. Hybrids between these genera could potentially combine the excellent cold hardiness and adaptability of Diervilla with diverse forms, foliage colors, and flower colors found in Weigela. Prior attempts to create intergeneric hybrids between these genera were unsuccessful and resulted in embryo abortion before seeds matured. To overcome this barrier, ovule culture and micropropagation procedures were used to develop intergeneric hybrids. Cleaved amplified polymorphic sequences (CAPS) analysis was used to verify hybrids. Intergeneric crosses, D. lonicera × W. middendorfiana, D. sessilifolia × W. florida (two clones), and D. lonicera × W. florida were attempted. Crosses of D. lonicera × W. middendorfiana did not produce viable hybrids. From the remaining three crosses, a total of 544 plants were obtained from 1278 ovules. About 85% of the 544 plants appeared very chlorotic or had low vigor, and senesced when transferred to multiplication medium. Only 80 of the 544 plants were successfully maintained in tissue culture, of which 10 have been successfully transferred ex vitro. CAPS analysis indicated that a majority of these plants were hybrids. Further studies are focused on improving tissue culture procedures and other methods to develop tetraploids to increase plantlet vigor and fertility.