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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Improvement of Citrus for Enhanced Resistance to Biotic and Abiotic Stresses

Location: Subtropical Insects and Horticulture Research

Title: Freeze response of citrus and citrus-related genotypes in a Florida field planting

Authors
item INCH, SHARON
item STOVER, ED
item DRIGGERS, RANDALL
item LEE, RICHARD

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 19, 2014
Publication Date: N/A

Interpretive Summary: A trial with 8 seedlings from each of 92 diverse citrus and citrus relatives was planted in East-central Florida. Seeds were obtained from the Citrus genebank in Riverside, California and the identifying numbers used below are those from the associated Citrus Variety Collection of the University of California. Unusually low temperatures (near -4°C each winter) for east central Florida were experienced during the winters of 2010 and 2011 and cold-injury was assessed each year. Defoliation and dieback were significantly greater in the winter of 2011 than in the winter of 2010. The winter in 2011 was preceded by a period of extraordinarily low temperatures in mid-December, with no period of cool temperatures to allow trees to acclimate. In 2010 the average defoliation was 53% ' 28% with little dieback, whereas in 2011 the average defoliation and dieback were 93% ' 17% and 51% ' 35%, respectively. Within the genus citrus several seedling groups had 16-24% dieback in 2011 and these were from parents C. reticulata (CRC 2590) (23%), C. sinensis (CRC 3858) (24%), C. maxima (CRC 3945) (16%), C. hassaku (CRC 3907 and 3942) (16% and 17%), C. aurantium (CRC 628 and 2717) (18% and 7%), C. taiwanica (CRC 2588) (21%), and C. neo-aurantium (C. obovoidea + C. unshiu graft chimera)(CRC 3816) (23%). Within other genera closely related to citrus, Poncirus trifoliata (CRCs 301, 3957, 3549, and 4007), Severinia buxifolia (CRC 1497), Bergera koenigii (CRC 3165), and Glycosmis pentaphylla (CRC 3285) had the least amount of dieback, all at less than 23%. Two seedling groups in a somewhat more distantly related subfamily (Casimiroa edulis and Zanthoxylum ailanthoides) had among the least amount of dieback (1% and 8% respectively). When considered by groups, the Citrons and Australian natives had the greatest amount of dieback in 2011, 68% and 65%, respectively. The trifoliates (Poncirus and hybrids) had the least dieback, ranging from 4%- 40%. The information from this study may be useful in citrus breeding targeting greater cold tolerance.

Technical Abstract: A test population consisting of progenies of 92 seed-source genotypes (hereafter called “parent genotypes”) of citrus and citrus relatives in the field in East-central Florida was assessed following natural freeze events in the winters of 2010 and 2011. Eight seedlings per parent genotype were planted in a randomized complete block design, however due to mortality the number of plants assessed in some genotype groups was reduced at some or all sampling dates. The citrus diseases huanglongbing and citrus canker were endemic in the planting, and may have influenced tree response to cold temperatures. Unusually low temperatures (near -4°C each winter) for east central Florida were experienced during the trial period. Defoliation and dieback were significantly greater in the winter of 2011 than in the winter of 2010. The winter in 2011 was preceded by a period of extraordinarily low temperatures in mid-December, with no period of cool temperatures to allow trees to acclimate. In 2010 the average defoliation was 53% ' 28% with little dieback, whereas in 2011 the average defoliation and dieback were 93% ' 17% and 51% ' 35%, respectively. Within the genus Citrus several progenies were identified that had 16-24% dieback in 2011 and these were from parent genotypes C. reticulata (CRC 2590) (23%), C. sinensis (CRC 3858) (24%), C. maxima (CRC 3945) (16%), C. hassaku (CRC 3907 and 3942) (16% and 17%), C. aurantium (CRC 628 and 2717) (18% and 7%), C. taiwanica (CRC 2588) (21%), and C. neo-aurantium (C. obovoidea + C. unshiu graft chimera) (CRC 3816) (23%). Within other genera in the Aurantiodeae, Poncirus trifoliata (CRCs 301, 3957, 3549, and 4007), Severinia buxifolia (CRC 1497), Bergera koenigii (CRC 3165), and Glycosmis pentaphylla (CRC 3285) had the least amount of dieback, all at less than 23%. The two species within the Toddalioideae subfamily of the Rutaceae (Casimiroa edulis and Zanthoxylum ailanthoides) had among the least amount of dieback (1% and 8% respectively). When considered by groups, the Citrons and Australian natives had the greatest amount of dieback in 2011, 68% and 65%, respectively. The trifoliates (Poncirus and hybrids) had the least dieback, ranging from 4%- 40%. The information from this study may be useful in Citrus breeding targeting greater cold tolerance.

Last Modified: 7/28/2014
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