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Eliezer S. Louzada and Chandrika Ramadugu

Grapefruit [Citrus ×aurantium (synonym C. ×paradisi)] is an important citrus commodity that originated in Barbados in the 17th century. Grapefruit is the youngest member of the genus Citrus. Most commercially important grapefruit cultivars arose through natural and induced mutations, not traditional breeding, of the white-fleshed and seedy Duncan grapefruit. Now, cultivars with a range of flesh colors exist; the pigmentation is correlated with lycopene content. A bud sport mutant of grapefruit discovered in Texas has a deep golden-colored flesh, significantly different from the typical reddish pigmentation. In this review, we discuss grapefruit’s journey from its origin in Barbados and its global establishment including production, marketing, drug interactions, cultivar development, genetic diversity, and commercially significant cultivars.

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Madhurababu Kunta, John V. da Graça, Nasir S.A. Malik, Eliezer S. Louzada, and Mamoudou Sétamou

The Asian citrus psyllid, Diaphorina citri Kuwayama, one of the known vectors for citrus greening disease or Huanglongbing (HLB) pathogens, has been present in Texas for over a decade, but the detection of the disease is recent. HLB has been confirmed in only two adjacent commercial citrus groves of grapefruit and sweet orange. A study was conducted to compare the population of Candidatus Liberibacter asiaticus (CLas) cells in different plant parts including peduncle, columella, leaves, seeds, young shoots, flower buds, flowers, and bark of 6-year-old known infected grapefruit and sweet orange trees. The bacterial population was estimated using a previously described grand universal regression equation Y = 13.82 – 0.2866X, where Y is the log of the target copy number and X is the Ct (threshold cycle) of the assay. Except for bark tissue, there was no significant difference in the concentration of CLas cells in other plant parts between the two cultivars. Within the cultivar, the bacterial concentration also varied with the plant part, with peduncle, columella, midrib having significantly higher titer of CLas compared with other plant parts. The obtained results here are in agreement with previous studies conducted on Florida samples, but the consistently lowest bacterial titer recorded in young shoots, leaf blade, and especially leaf margins relative to the midrib has never been previously reported.

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Eliezer S. Louzada, Hilda Sonia de Rio, Allison J. Abell, Gerson Peltz, and Michael W. Persans

Hispanics lag behind all other U.S. ethnic groups in education, and are especially poorly represented in science careers. Undergraduate research is an efficient method to attract undergraduate students to science, and many universities are taking advantage of this; however, much still needs to be done to fully explore its potential. In 2000, Texas A&M University-Kingsville, in collaboration with the University of Texas at Brownsville and the University of Texas Pan-American, initiated a undergraduate research internship program in citrus biotechnology to channel Hispanic undergraduate students into graduate education. To date, 51 internships have been provided, and 20 students have been channeled into graduate school, including four at the doctoral level. Most were first-generation college students.

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Claudine M. Bona, Jean H. Gould, J. Creighton Miller, David M. Stelly Jr., and Eliezer S. Louzada

The highly appreciated Euvitis subgenera species (2n=38) are very susceptible to pests and diseases. Tolerance/resistance may be found in the closely related Vitis rotundifolia cultivars (2n=40), but the poor rooting characteristic of this species is a problem, and conventional crossings between Euvitis and V. rotundifolia are complicated because of different chromosome numbers. Therefore, somatic hybridization may be an alternative for gene transference between these species. The establishment of an efficient in vitro procedure may facilitate future genetic manipulations. Furthermore, in vitro success may be an indicative of protoplast totipotency. The goal of this research was to test 11 cultivars from different species for their in vitro cultivation and protoplast isolation capacity. Different doses of benzyladenine (BA) were tested and explants were cultivated in both Lloyd and McCown's Woody Plant Medium (WPM) and Murashige and Skoog medium (MS). We established an efficient in vitro procedure and plants of C. sauvignon, Syrah, SV 12-375, Scuppernong, Magnolia, Higgens and B. beauty were regenerated. No rooting problem was observed in vitro. Black spanish and Herbemont callus were kept in vitro, but plants were not regenerated. SV-12327 and Jumbo died. WPM was more efficient than MS for most cultivars. The V. vinifera cultivars C. sauvignon and Syrah developed well in both media. Protoplast isolation was more efficient using leaves rather than callus or suspension cells. BA at 3 μM·L-1 induced organogenesis while 10 μM·L-1 induced callogenesis except for Syrah, where 1 μM·L-1 induced organogenesis. Protoplasts were isolated from Herbemont and C. sauvignon and microcallus were obtained.

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Jude W. Grosser, Frederick G. Gmitter Jr., J.L. Chandler, and Eliezer S. Louzada

Protoplasm culture following polyethylene glycol-induced fusion resulted in the regeneration of tetraploid somatic hybrid plants from the following attempted parental combinations: Cleopatra mandarin (Citrus reticulata Blanco) + Argentine trifoliate orange [Poncirus trifoliata (L.) Raf.]; `Succari' sweet orange [C. sinensis (L.) Osb.] + Argentine trifoliate orange; sour orange (C. aurantium L.) + Flying Dragon trifoliate orange (P. trifolita); sour orange + Rangpur (C. limonia Osb.); and Milam lemon (purported sexual hybrid of C. jambhiri Lush × C. sinensis) + Sun Chu Sha mandarin (C. reticulate Blanco). Protoplasm isolation, fusion, and culture were conducted according to previously published methods. Regenerated plants were classified according to leaf morphology, chromosome number, and peroxidase, phosphoglucomutase, and phosphoglucose isomerase leaf isozyme profiles. All of the somatic hybrid plants were tetraploid, as expected (2n = 4x = 36), and all five selections have been propagated and entered into commercial citrus rootstock trials.

Open access

Madhurababu Kunta, Sandy Chavez, Zenaida Viloria, Hilda S. del Rio, Madhavi Devanaboina, George Yanev, Jong-Won Park, and Eliezer S. Louzada

Seeds from four citrus rootstocks including sour orange, Bitters-C22 citrandarin, Sarawak pummelo × Rio Red grapefruit, and Sarawak pummelo ×Bower mandarin were exposed to high inoculum levels of Phytophthora nicotianae to screen for tolerance. Inoculation of pregerminated seeds (PGIS) and non-PGIS was carried out. The average P. nicotianae propagule counts from the soil samples where these seedlings were raised ranged from 424 to 1361 colony forming units/cm3. The proportion of live to dead plants was recorded at 11 months postinoculation, which showed that Sarawak ×Bower performed significantly better than other rootstocks. Evaluation of the rootstocks 18 months postinoculation resulted in only one surviving sour orange plant, which suggests potential rootstock resistance.

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Eliezer S. Louzada, Jude W. Grosseti, Frederick G. Gmitter Jr., Beatriz Nielsen, J.L. Chandler, Xiu Xin Deng, and Nicasio Tusa

Protoplast culture following polyethylene glycol-induced fusion resulted in the regeneration of vigorous tetraploid somatic hybrid plants from eight complementary parental rootstock combinations: Citrus reticulata Blanco (Cleopatra mandarin) + C. aurantium L. (sour orange), C. reticulata (Cleopatra mandarin) + C. jambhiri Lush (rough lemon), C. reticulata (Cleopatra mandarin) + C. volkameriana Ten. & Pasq. (Volkamer lemon), C. reticulata (Cleopatra mandarin) + C. limonia Osb. (Rang-pur), C. sinensis (L.) Osb. (Hamlin sweet orange) + C. limonia (Rangpur), C. aurantium (sour orange) + C. volkameriana (Volkamer lemon) zygotic seedling, C. auruntium hybrid (Smooth Flat Seville) + C. jambhiri (rough lemon), and C. sinensis (Valencia sweet orange) + Carrizo citrange [C. paradisi Macf. × Poncirus trifoliata (L.) Raf.]. Diploid plants were regenerated from nonfused callus-derived protoplasts of Valencia sweet orange and Smooth Flat Seville and from nonfused leaf protoplasts of sour orange, Rangpur, rough lemon, and Volkamer lemon. Regenerated plants were classified according to leaf morphology, chromosome number, and leaf isozyme profiles. All somatic hybrid plants were tetraploid (2n = 4× = 36). One autotetraploid plant of the Volkamer lemon zygotic was recovered, apparently resulting from a homokaryotic fusion. These eight new citrus somatic hybrids have been propagated and entered into field trials.

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Thomas M. Gradziel, Robert J. Knight Jr., William Reid, Chad E. Finn, John R. Clark, Eliezer S. Louzada, and Kim E. Hummer