variety CRC3306A for use in these experiments. The sequencing of CsLFY and CsAP1 was supported by UC Riverside Genomics Institute Core grants to Drs. C. Lovatt and L. Walling. The authors acknowledge partial support from the Citrus Research Center and
1 Assistant professor, Instituto Tecnológico y de Estudios Superiores de Monterrey, Campus Monterrey, Dept. Centro de Estudios del Agua, Ave. Eugenio Garza Sada 2501, Aulas 7-316, Col. Tecnológico, 64849 Monterrey, N.L. This research was supported
The effect of shoot angle on dry matter production and distribution was determined for seedlings of peach over 7 or 11 weeks’ growth and of sweet orange over 12 weeks’ growth. The effect of tilting the pots was also determined for sweet orange. For peach, total weight and leaf weight was greatest and the proportion of root was least for plants with vertical shoots. In the case of citrus, mean plant weights did not differ significantly but the proportion of leaves increased and the proportion of roots again decreased for plants with vertical shoots. Shoot inclination affected the proportion of the growth increment used to develop the root system in both peach and orange. Tilting the pots had no effect on distribution of dry matter in sweet orange.
A procedure for the extraction and fractionation of nucleic acids from citrus tissues was developed. Typical elution profiles of nucleic acids extracted from leaves, root tips, flowers, and fruits at different stages of development showed the well-known peaks of s-RNA, DNA, lr-RNA, and hr-RNA. In flowers and, especially, in young fruits the additional X-RNA peak was also present following the hr-RNA peak. The level of nucleic acids decreased markedly in the young fruit on the dry matter basis during the first 3 months of growth, mostly due to decrease in hr-RNA. During maturation the RNA fractions in the albedo decreased, while it increased in the flavedo due to increase in hr-RNA content. The fast growth of the young fruit apparently is accompanied by intensive metabolization or turnover of nucleic acids, rather than by dilution.
Economically, citrus is the second most-important fruit crop grown worldwide; thus germplasm conservation of commercial cultivars, as well as of wild relatives, is essential. Presently, citrus germplasm has been conserved mainly in field genebanks. This approach is helpful; however, it is costly, exposes germplasm to climatic and biological hazards, and is not a long-term conservation system. Cryopreservation (conservation in liquid nitrogen, at –150°C to –196°C) is a technique that can ensure long-term storage of plant material. Attempts to cryopreserve citrus are restricted to a few reports, but the results obtained are encouraging. The basic purpose of this study is to define cryopreservation protocols for embryo axes and axillary buds of `Pineapple' sweet orange using the encapsulation-dehydration method. Embryo axes encapsualted in Na-alginate beads, precultured with high levels of sucrose and dehydrated over silica gel before freezing in liquid nitrogen had 60% survival. No survival was obtained for buds treated the same way, however buds isolated from plants acclimated at 0°C over a 30-day period survived exposure to –20°C when slow cooled at 2°C/hour. Additional experiments will combine cold acclimation, slow cooling and pre-treatment with sugars and other chemical compounds as an attempt to enhance cold hardiness of axillary buds and obtain survival after freezing in liquid nitrogen. Different approaches will be used to increase embryo axes survival rates.
This study investigated the effect of irrigation treatments and time of foliar applications of low-biuret urea on yield of 30-yr-old navel orange trees grown under optimal N fertilization. The experiment was carried out at the Agricultural Experiment Station of the University of California, Riverside, using split plot design with 12 replications. The two irrigation treatments were the mainplots and the urea applications were the subplots. Irrigation was withheld from one set of trees from October to March, the other set was irrigated according to commercial practice. Foliar-urea (0.17 kg/tree) was applied in November, December, January, or February.
The results of the first year showed no significant differences between irrigation treatments with regard to total fruit weight or total number of fruit per tree, All trees receiving urea had significantly higher fruit weight and fruit number per tree than the control trees. The specific time of urea application had no significant effect.
With respect to fruit size distribution, the irrigated treatment resulted in a significantly higher number of fruit of size 7.0-8.0 cm (box sizes 88-72). Generally, the non-irrigatd trees had more fruit of size 6.0 cm or less. No interaction between irrigation treatments and foliar urea sprays was observed.
The ability of arginine (50 mM), putrescine (10 and 20 mM), and spermidine (10 and 20 mM) to enhance low temperature stressed-induced flowering of 5-year-old container-grown `Washington' navel orange trees was evaluated. The metabolites were applied to the foliage at the end of the 4-week low-temperature treatment of 8-h days at 10°C and 16-h nights at 7°C; the trees were then moved to warmer conditions.
All treatments had a positive effect on floral intensity. Putrescine (20 mM) and spermidine (10 mM) significantly increased (P = 0.05) total flower number and both the number and proportion of leafless inflorescences per tree. However, the number of floral shoots per tree, as well as the number of leafy inflorescences and number of vegetative shoots were not significantly influenced by the metabolites.
The results suggest that polyamines are important to the development of flowers, but not leaves, along the axis of the inflorescence.
has been regulated since 2008 as a result of concerns of M. paniculata being a reservoir of C Las for commercial citrus ( Clark, 2007 ). C Las transmission between Citrussinensis (L.) Osbeck var. ‘Madam Vinous’ and M. paniculata by ACP has