Postharvest Application of Acibenzolar-S-Methyl Activates Salicylic Acid Pathway Genes in Kiwifruit Vines

The plant defence inducer Actigard^® (acibenzolar-S-methyl [ASM]) is applied before flowering and after fruit harvest to control bacterial canker in kiwifruit caused by Pseudomonas syringae pv. actinidiae. Pre-flowering application of ASM is known to upregulate defence gene expression; however, the effect of postharvest ASM on defence gene expression in the vine is unknown. In this study, the expression of eight "defence marker" genes was measured in the leaves of Actinidia chinensis var. chinensis, "Zesy002," and Actinidia chinensis var. deliciosa, "Hayward," vines after postharvest treatment with ASM and/or copper. There were two orchards per cultivar with harvest dates approximately three weeks apart for investigating potential changes in responsiveness to ASM during the harvest period. In all trials, postharvest ASM induced the expression of salicylic-acid-pathway defence genes PR1, PR2, PR5, BAD, DMR6, NIMIN2, and WRKY70. Gene upregulation was the greatest at 1 day and 7 days after treatment and declined to the control level after 3 weeks. In "Zesy002", the ASM-induced response was greater at the early harvest site than at the late harvest site. This decline was concomitant with leaf yellowing and a reduction in RNA yield. Effects of postharvest ASM on gene expression did not persist into the following spring, nor were vines conditioned to respond more strongly to pre-flowering ASM application.

First Report of Pseudomonas syringae pv. actinidiae the Causal Agent of Bacterial Canker of Kiwifruit on Actinidia arguta Vines in New Zealand

Actinidia arguta is commercially grown in New Zealand and few other countries; the fruit are sometimes sold as kiwiberry or hardy kiwi. In New Zealand, two biovars of Pseudomonas syringae pv. actinidiae have recently been found to cause bacterial canker on both A. chinensis and A. deliciosa, which produce the yellow and green fleshed kiwifruit, respectively (4). In November 2011, in a commercial orchard in the Bay of Plenty, New Zealand, A. arguta 'Tahi' and 'Rua' showed small angular necrotic leaf spots. About 50% of the vines randomly located throughout the orchard showed symptoms. Canker or shoot dieback were not detected on any of the infected plants. Four strains, labeled 13093 to 13096, were isolated onto King's B medium (KB) from leaves selected from four different plants showing symptoms. These four strains were gram-negative, induced a hypersensitive reaction when infiltrated in tobacco plants, lacked cytochrome c oxidase, arginine dehydrolase, and urease activity, and were unable to hydrolyze esculin, starch, and gelatine, and to induce ice nucleation. When plated on KB, these strains showed the same weak fluorescence associated with some strains of P. syringae pv. actinidiae (4). All these characteristics support identification of the strains as P. syringae pv. actinidiae. Using P. syringae pv. actinidiae-specific primers PsaF1/R2 (2), the expected 280-bp fragment was amplified by PCR from genomic DNA extracted from the four strains. The four amplicons were sequenced (GenBank Accession Nos. KF206138 to 41) and found to be 100% identical to each other and to the corresponding DNA fragment of the pathotype strain, ICMP 9617 (AY342165). A similar conclusion was reached using the duplex PCR targeting the ompP1 and the avrD genes (1); two amplicons of 492 and 226 bp were obtained with each of the four strains as expected for P. syringae pv. actinidiae. The DNA sequence of the 492-bp amplicon (KF206134 to 37) was 100% identical to that of strains of P. syringae pv. actinidiae, such as Psa 10627 (JQ934475.1). Strain 13094 isolated from A. arguta and pathotype strain ICMP 9617 were sprayed at a concentration of 3 × 10⁹ cfu/ml on to the undersides of leaves of three 6- to 8-week-old seedlings of A. chinensis'Hort16A' and three similar seedlings of A. deliciosa 'Bruno.' Those are the conditions under which the pathogenicity of strains of P. syringae pv. actinidiae is usually evaluated (4). After 2 weeks of incubation, small necrotic angular spots were observed on all plants inoculated with 13094 or ICMP 9617 but not on the water-treated control plants. The bacteria isolated from those necrotic spots had the same morphological characteristics on KB as P. syringae pv. actinidiae and gave a 280-bp amplicon after PCR with the PsaF1/R2 primers. Leaves of two rooted cuttings of A. arguta'Tahi' were spray inoculated with strain 13094 at a concentration of 2.7 × 10⁹ cfu/ml or with water. Necrotic spots developed on leaves 1 week after inoculation. No spots developed on the water-treated plants. The bacteria isolated from those necrotic spots had the same morphological characteristics on KB as P. syringae pv. actinidiae and gave a 280-bp amplicon after PCR with the PsaF1/R2 primers. Isolation of P. syringae pv. actinidiae from A. arguta has been reported only once before (3). This is this is the first report of P. syringae pv. actinidiae being isolated from A. arguta vines in New Zealand. This limited outbreak did not lead to any loss of production and since then only very few symptoms have been observed in this particular orchard. References: (1) A. Gallelli et al. J. Plant Pathol 93:425, 2011. (2) J. Rees-Gorge et al. Plant Pathol. 59:453, 2010. (3) K. Ushiyama et al. Ann. Phytopath. Soc. Japan 58:476, 1992. (4) J. L. Vanneste et al. Plant Dis. 97:708, 2013.

Identification, Virulence, and Distribution of Two Biovars of Pseudomonas syringae pv. actinidiae in New Zealand

Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker of kiwifruit, was detected for the first time in New Zealand in November 2010. Only in Bay of Plenty, one of the four regions where this pathogen had been detected, did symptoms evolve beyond leaf spots, resulting in cane die-back, wilting of canes, and canker, sometimes leading to death of the vine. Molecular analysis (cts haplotype and BOX-polymerase chain reaction [PCR] electrophoretic pattern) of strains isolated from different regions of New Zealand revealed that two biovars could be distinguished. They have been called biovar 3 and biovar 4 to differentiate them from strains from Japan (biovar 1) or Korea (biovar 2), which have a different cts haplotype or a different BOX-PCR pattern. Biovars 3 and 4 displayed different degrees of virulence, as measured by their ability to cause leaf spots on young, potted kiwifruit plants. Biovar 3, which has also been present in Italy since 2008 and in France, was found in the Bay of Plenty, where cane diebacks were observed. In contrast, no symptoms other than leaf spots have been observed in orchards where strains of biovar 4 have been isolated. We report the distribution and the disease progression of biovars 3 and 4 in New Zealand.

First Report of Pseudomonas syringae pv. actinidiae, the Causal Agent of Bacterial Canker of Kiwifruit in France

In June 2010, young plants of kiwifruit growing in the French regions of Rhone-Alpes (Actinidia deliciosa 'Summer') and Aquitaine (A. chinensis 'Jintao') showed small, angular, necrotic leaf spots and cankers on some canes that was sometimes associated with production of a red exudate. Most of the affected canes died, and in a few cases after a few months, the entire plant died. Symptoms were consistent with Pseudomonas syringae pv. actinidiae, a bacterium that affects several species of Actinidia (A. deliciosa and A. chinensis, the two most important commercial species of kiwifruit). A recent outbreak of this disease is devastating the Italian kiwifruit industry. Bacterial colonies were isolated on King's medium B (KB) from leaf spots and infected canes. Three isolates from Aquitaine and 10 from Rhone-Alpes were retained for further characterization. The 13 isolates were gram negative, induced a hypersensitive reaction when infiltrated in tobacco plants, did not have a cytochrome c oxidase, an arginine dehydrolase or urease activity, did not hydrolyze esculin, starch, or gelatine, and did not induce ice nucleation. When plated on KB, these strains did not show strong fluorescence usually associated with strains of P. syringae. Complete lack of fluorescence reported for the pathotype strain ICMP 9817 has not been observed for those strains. They showed the same weak fluorescence as the strains of P. syringae pv. actinidiae recently isolated from Italy. Those characteristics match those of strains of P. syringae pv. actinidiae (3). Using total DNA of the 13 strains, the pathotype strain, and primers PsaF1/R2 (2), a 280-bp fragment was amplified by PCR, supporting the strains as being P. syringae pv. actinidiae. The amplicon from 6 of the 13 strains was sequenced and found to be 100% similar to the corresponding DNA fragment of the pathotype strain ICMP 9617 (GenBank AY342165). Partial sequences of 1,381 bp of the 16S rDNA gene of four of the six isolates, three strains isolated from Rhone-Alpes and one strain isolated from Aquitaine, were obtained by amplification with primers 27_f and 1492_r (1). Except for the sequence of strain 181, which was isolated from Aquitaine and had a 1 bp difference (GenBank JF323026), the other sequences were 100% identical to each other (GenBank JF323027 to JF323029). These four sequences were 99% identical to the 16SrDNA sequences of ICMP 9617, the pathotype strain of P. syringae pv. actinidiae (GenBank AB001431). These four strains and the pathotype strain were sprayed (1 × 10⁹ CFU/ml) on leaves of four 6- to 8-week-old seedlings of A. chinensis each. After 4 days, small, necrotic, angular spots were found on all plants inoculated with those four strains and the pathotype strain. No symptoms were found on plants treated with water only. From those leaf spots, bacteria that had all the characteristics of P. syringae pv. actinidiae (as previously described) were isolated. Recently, two different haplotypes for the housekeeping gene cts were described for P. syringae pv. actinidiae (4), the strains isolated from France belong to the haplotype I. This is the same haplotype to which strains isolated from the recent Italian outbreak also belong. To our knowledge, this is the first report of bacterial canker of kiwifruit in France. References: (1) V. Gurtler and V. A. Stanisich. Microbiology 142:3 1996. (2) J. Rees-George et al. Plant Pathol. 59:453, 2010. (3) Y. Takikawa et al. Ann. Phytopathol. Soc. Jpn. 55:437, 1989. (4) J. L. Vanneste et al. N.Z. Plant Prot. 63:7, 2010.

First Record of Bacterial Crown Rot of Papaya (Carica papaya) Caused by an Erwinia papayae-Like Bacterium in the Kingdom of Tonga

Symptoms resembling papaya bacterial crown rot (1,3) attributed to Erwinia papayae were first observed on 'Waimanalo' and 'Solo Sunrise' papaya on the island of Tongatapu, Kingdom of Tonga in July 2009. Spreading, dark green, water-soaked lesions formed on juvenile stem tissue and developed into a foul-smelling, wet rot that destroyed large sections of the stem. Coalescing, brown, angular, marginal, and intercostal lesions killed large areas of the lamina. Elongated lesions on petioles resulted in breakage and leaf death. Symptoms on stems typically moved toward the crown with the growing point being killed or the whole crown breaking off at a canker below. Isolations at 28°C on King's medium B (KB) yielded slow-growing, raised, white, mucoid colonies that produced a conspicuous, nondiffusable blue pigment in the medium. Two-day-old suspensions (1 × 10⁸ CFU/ml) of two cultures were injected into juvenile stem tissue, petioles, and laminae of four healthy papaya seedlings of 'Solo Sunrise' with a sterile 1-ml insulin syringe. Sterile water was used as a negative control. Typical water-soaked lesions appeared at all bacterial inoculation sites on all plants within 5 days but not on controls. Pigment-producing colonies similar to those used for inoculation were reisolated from four different stem lesions. Bacteria isolated from diseased tissues were gram negative, facultative anaerobes, oxidase negative, nonfluorescent on KB, induced a hypersensitive reaction on tobacco leaves, but could not cause soft rot on potato slices. Those characteristics, combined with blue pigment production, are consistent with the bacterium E. papayae. A partial sequence of the 16S rDNA gene of ~804 bp was amplified from four Tongan isolates (ICMP18248-18251) using primers 27f and 1492r (4). Sequences of these strains were 100% identical to each other (GenBank Nos. HQ286366-HQ286369), 99 and 98% identical to the 16SrDNA sequences of E. mallotivora strains LMG2708 (Z96084.1) and DSM4565 (AJ233414.1) respectively, and 97% identical to the 16SrDNA sequence of E. papayae strain NCPPB 4294 (AY131237.1). E. mallotivora and E. papayae cause different diseases, a leaf spot on Mallotus japonicus (2) and bacterial canker on papaya, respectively. They are closely related and in the laboratory are distinguished by only very few biochemical characteristics (1). E. papayae produces a blue pigment on KB and can utilize arabinose but not mannitol. E. mallotivora does not produce a blue pigment and can utilize mannitol but not arabinose. The four Tongan strains produced a blue pigment and could utilize mannitol and arabinose. Symptoms caused by the strains isolated from Tonga are typical of those caused by E. papayae and the strains identified share most of the characteristics of E. papayae. Because the Tongan strains were able to utilize mannitol as well as arabinose and their 16S rDNA was only 97% similar to E. papayae, these strains are referred to as an E. papayae-like bacterium. The taxonomic position of these isolates will be resolved with techniques such as Multilocus Sequence Typing analysis. To our knowledge, this is the first report of this highly destructive papaya disease in the Kingdom of Tonga and of a pathogen closely related to E. papaya in the country. References: (1) L. Gardan et al. Int. J. Syst. Bacteriol. 54:107, 2004. (2) M. Goto. Int. J. Syst. Bacteriol. 26:467, 1976. (3) N. H. Maktar et al. New Dis. Rep. 17:4, 2008. (4) F. Martin-Laurent et al. Appl. Environ. Microbiol. 67:2354, 2001.

An investigation into a possible relationship between vitamin D, parathyroid hormone, calcium and magnesium in a normally pigmented and an albino rural black population in the Northern Province of South Africa

Vitamin D levels are important in the management of patients with various disorders of calcium metabolism associated with rickets, osteomalacia, osteodystrophy osteoporosis and hypoparathyroidism. 82 albinos and 58 normally pigmented children resident at the Siloe School for the Visually Impaired were sampled. Blood samples of fasting subjects were collected over a two-day period and analyzed for vitamin D, parathyroid hormone, plasma calcium and both plasma and red blood cell magnesium measurements. The height and weight of each subject was also recorded. The results are discussed in relation to the different skin pigmented groups, for specific age groups, sex and visual status. Statistical outliers were excluded from the results. It appears that the Albino group has significantly (p = 0.06) higher vitamin D levels against the background of a similar dietary intake and similar exposure to sunlight/day length. Thus black children/subjects require a significantly higher intake of vitamin D to attain the same level as their Albino counterparts. In spite of significantly higher vit D levels, the other homeostatic control mechanisms were not altered (i.e., PTH levels are similar in both groups). This study supports the postulate that a dark complexion predisposes to sub-optimal vit D status.