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Xuetong Fan, Kimberly J. Sokorai, Brendan A. Niemira, Robert S. Mills and Mark Yueqian Zhen

Irradiation of Iceberg lettuce was recently approved by the U.S. Food and Drug Administration (FDA) to enhance microbial safety and to extend shelf life at doses up to 4 kGy. However, the radiation tolerance of whole head lettuce is unclear. The present study was conducted to investigate the effects of gamma irradiation on the quality of Iceberg lettuce and explore means to reduce irradiation-induced disorders. Irradiation (0.5 and 1.0 kGy) induced symptoms similar to russet spotting and other discolorations (pink ribs, rusty brown, and vein browning) in both external and internal leaves during post-irradiation storage in air at 4 °C. Irradiation in the absence of oxygen or pretreatment with 1 ppm 1-methylcyclopropene had little effect on the irradiation-induced tissue discoloration. However, low oxygen atmosphere when maintained during the entire 14-day storage almost eliminated the disorders. Compared with non-treated control, irradiation created significantly lower headspace O2 and higher CO2 levels in the packages, indicating that irradiation promoted respiration. Our results suggest that modified atmosphere (MA) packaging could be used to mitigate irradiation-induced disorders in Iceberg lettuce.

Open access

Natalia Salinas, Zhen Fan, Natalia Peres, Seonghee Lee and Vance M. Whitaker

FaRCa1 is a major locus conferring resistance to anthracnose fruit rot (AFR) caused by Colletotrichum acutatum, an important pathogen of strawberry (Fragaria ×ananassa). The objective of this study was to characterize the effects of FaRCa1 on anthracnose root necrosis (ARN) via root inoculations and DNA marker characterization of the locus. A subgenome-specific high-resolution melting (HRM) marker for an insertion/deletion (InDel) near FaRCa1 was designed using the ‘Camarosa’ octoploid reference genome. The marker was used to genotype cultivars and advanced selections studied in two seasons. A root disease screening method was developed in which roots were cut and dipped in a spore suspension before planting, using a mixture of three local isolates of the C. acutatum species complex. ARN was indirectly scored by calculating image-based leaf area differences among inoculated and noninoculated plants. The allele of FaRCa1 conferring resistance to AFR also conferred a significant reduction in ARN. Thus, a robust and easily scored DNA test is now available to breeders for selecting for resistance to both the fruit and root forms of strawberry anthracnose.

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Li-Xiao Yao, Yong-Rui He, Hai-Fang Fan, Lan-Zhen Xu, Tian-Gang Lei, Xiu-Ping Zou, Ai-Hong Peng, Qiang Li and Shan-Chun Chen

Ferric chelate reductase (FRO) is a critical enzyme for iron absorption in strategy I plants, reducing Fe3+ to Fe2+. To identify FRO family genes in the local Citrus junos cultivar Ziyang Xiangcheng and to reveal their expression model, the citrus (Citrus sp.) genome was searched for homologies of the published sequence CjFRO1. Five FROs were found, including CjFRO1; these were named CjFRO2, CjFRO3, CjFRO4, and CjFRO5, respectively, and cloned via reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) PCR. The deduced amino acid sequences of five CjFROs contained flavin adenine dinucleotide (FAD)-binding motifs, nicotinamide adenine dinucleotide (NAD)-binding motifs, and 6–10 transmembrane domains, with isoelectric points between 6.73 and 9.46, and molecular weights between 67.2 and 79.9 kD. CjFRO1 and CjFRO2 were predominantly found in the aboveground parts of C. junos, with CjFRO1 highly expressed in leaves, and CjFRO2 largely expressed in stems and leaves. CjFRO3 was less expressed in roots, stems, and leaves. CjFRO4 and CjFRO5 were predominately found in roots. Under iron-deficient conditions, CjFRO4 was significantly and specifically increased in the roots of C. junos, whereas CjFRO1 was upregulated in the roots and leaves.

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Vance M. Whitaker, Luis F. Osorio, Natalia A. Peres, Zhen Fan, Mark Herrington, M. Cecilia do Nascimento Nunes, Anne Plotto and Charles A. Sims

Open access

Vance M. Whitaker, Natalia A. Peres, Luis F. Osorio, Zhen Fan, M. Cecilia do Nascimento Nunes, Anne Plotto and Charles A. Sims