Rough lemon seedlings [Citrus limon (L)] were hydroponically-cultured in complete Shive's nutrient solution (+K) or in Shive's nutrient solution with potassium omitted (-K) for a period of eight months. Fresh and dry weight of whole -K plants were reduced 4-fold (P<0.01). Nitrogen metabolism was monitored during this period in young, fully expanded leaves. Results showed that leaves of -K plants accumulated 2.5-fold more NH3-NH4 + than +K plants (P<0.01) and exhibited a concomitant increase in both activity of the de novo arginine biosynthetic pathway (2.5-fold) and free-arginine concentration (3.5-fold; P<0.001). Leaf proline content of -K plants increased 1.6-fold (P<0.05), while putrescine content increased 10-fold. Arginine decarboxylase activity was accelerated in -K plants.
Yusheng Zheng and Carol J. Lovatt
S. B. Boswell, R. M. Burns, and H. Z. Hield
Sprays of a plant growth regulator ammonium ethyl carbamoylphosphonoate (Krenite), applied to top regrowth of mature Lisbon lemon trees [Citrus limon (L.) Burmann] resulted in significant inhibition of growth for over 1 year. At concentrations above 0.2% there was excessive foliar and small branch damage.
S. B. Boswell, T. W. Embleton, W. W. Jones, and L. L. Summers
Sprays of ammonium ethyl carbamoyl-phosphonoate (Krenite), applied to the tops of mature Lisbon lemon trees [Citrus limon (L). Burml.] resulted in significant inhibition of re-growth for over 3 years. One spray increased yield over the control trees (hand topped annually), while 2 sprays reduced yield. The sprays did not effect the N concentration in the leaves.
S. Singh, B.K. Ray, S. Bhattacharyya, and P.C. Deka
Multiple shoots were obtained from shoot tips (2 to 3 mm) derived from mature plants (5 to 6 years old) of Citrus reticulata Blanco cv. Khasi mandarin and C. limon Burm.f. cv. Assam lemon when cultured on Murashige and Skoog (MS) medium, supplemented with (mg·liter-1) 1.0 BAP, 0.5 kinetin, and 0.5 NAA. Root induction was observed when 7-week-old single shoots (≈ 2 cm long) of both Citrus species were cultured on MS medium supplemented with (mg·liter-1) 0.25 BAP, 0.5 NAA, and 0.5 IBA. These plantlets were successfully established in the soil. Chemical names used: naphthalene acetic acid (NAA), indole 3-butyric acid (IBA), and benzylamino purine (BAP).
B. L. Wild, W. B. McGlasson, and T. H. Lee
Lemons (Citrus limon (L.) Burm. f.) were stored for up to 27 weeks at 10°C in air and in an atmosphere of 3 to 5% O2 and 0.1 to 0.2% CO2, with and without an ethylene absorbent. Mold incidence was high in controlled atmosphere (CA) storage where ethylene accumulated, but removal of ethylene reduced its development. CA storage improved retention of green color in lemons.
R. E. McDonald, T. T. Hatton, and R. H. Cubbedge
‘Bearss’ lemons (Citrus limon Burm f.) stored 21 days at 1°C and held 14 days at 21° sustained 15% chilling injury (Cl) compared to 1% after 10° storage and 21° holding period. Decay, predominantly caused by Penicillium digitatum Sacc., was negligible during storage at either 1° or 10°, but developed during the holding period at 21°. After storage at 1° or 10° plus 2 weeks at 21°, decay averaged 7.4% and 0.7%, respectively. Fruit size, method of curing, and presence of oleocellosis were not related to Cl or decay development.
R. E. McDonald
Film wrapping or holding for 3 days at 21°C reduced chilling injury (CI) and decay of ‘Bearss’ lemons (Citrus limon Burm. f.) stored at 1° for 21 days plus 14 days at 21°. Prestorage treatments of 40% CO2 for 3 days at 21° or dips in 2%, 10%, or 20% vegetable oils were not effective in reducing CI or decay during a similar storage and holding period. The use of 10 μl·liter−1 ethylene to degreen lemons significantly increased CI and decay compared to degreening without ethylene, especially when lemons were stored at 1°.
Eliahou Cohen, Susan Lurie, and Yavin Shalom
Mature green lemon (Citrus limon Burm.) fruits are degreened commercially with ethylene to enhance yellow color development and improve marketing quality. This treatment often results in the development of a peel disorder called red blotch, a superficial reddish-brown discoloration, which may cover most of the fruit peel. We found that degreening at 30°C, instead of the recommended temperature of 25°, eliminated the disorder. Similarly, a predegreening treatment of dipping the fruit in the antioxidant ethoxyquin (“Stop Scald”) prevented red blotch development. The high temperature and the antioxidant may act on oxidative enzyme systems, which are apparently causative factors of the disorder.
M. G. Bausher and G. Yelenosky
Different concentrations and methods of applying paclobutrazol on citrus plants [Citrus limon (L.) Burm. f.] under greenhouse conditions suggest 102 ppm (a.i.) foliar sprays or 20 mg per 2.5 liter pot are threshold concentrations for visible change in growth and development. Most apparent was reduced shoot extension, largely the result of shortened internodes. The leaves were smaller than those on untreated plants but little changed in length/width ratios. Loss of mass (weight) was mostly in the main stem and primary root. The most effective application method was as a soil drench which induced changes in the root as well as the tops of plants. As a stem-sprout inhibitor, paclobutrazol was less effective than “Tre-Hold.” Chemical names used: β-[(4-chlorophenyl)methyl-α-(l,l-dimethylethyl)-1H,2,4-triazole-l-ethanol (paclobutrazol); 1.15% ethyl 1-naphthalene acetate (“Tre-Hold”).
Roy E. McDonald
Chilling injury (CI) of lemons (Citrus limon Burm. f.) was reduced by temperature-conditioning at 10, 15, 21, or 27C immediately before storage at 1C. CI was less severe in lemons temperature-conditioned for 7 vs. 3 days. However, the process is not recommended for avoiding CI in lemons stored at low temperatures because of the wide range in treatment effects. Following conditioning at 21 and 27C, putrescine concentrations increased in flavedo tissue and were also higher in fruit after storage at 1C than at 10C, regardless of conditioning temperature. After holding fruit for 2 weeks at 21C, putrescine levels were higher in lemons that had been stored at 10C than in those stored at 1C. Prestorage temperature-conditioning did not affect spermidine levels, which tended to be higher in fruit stored at 10C than at 1C after storage and subsequent holding at 21C.