Combining apetalous parthenocarpy with columnar growth habit in apple

Summary ‘Wijcik’, a sport of ‘McIntosh’ with columnar growth habit, was crossed with ‘Wellington Bloomless’, which has apetalous flowers and bears parthenocarpic seedless fruit if not pollinated. The seedlings segregated for columnar versus normal habit but all had normal flowers and fruit. Four columnar seedlings were crossed with ‘Spencer Seedless’, another apetalous cultivar, and the resulting seedlings segregated not only for plant habit but also for apetalous versus normal flowers, approximately 1 : 1. Thus apetaly is controlled by a recessive gene, for which the symbolape is proposed. Apetalous columnar apples may be useful for planting in very high density orchards, cropping without pollination and thus not dependent on bees, pollinator varieties and warm weather at flowering time; moreover, being seedless they may avoid biennial bearing tendencies that are attributable to developing seeds inhibiting fruit bud formation.     

Correlation of ribonuclease zymograms and incompatibility genotypes in almond

Proteins were extracted from styles of 29 self-incompatible cultivars of almond and separated using non-equilibrium pH gradient electro-focusing, and the gels were stained for ribonuclease activity. Mutually incompatible cultivars had similar banding patterns and, for the 24 cultivars already genotyped in France or California, the bands correlated well with the reported alleles. The band corresponding to S₁ of the French labelling system was indistinguishable from that corresponding to S_b of the Californian labelling system, and a controlled cross confirmed that these alleles are identical. The band corresponding to the Californian S_a was distinct from the bands corresponding to French alleles and, to harmonise the allele labels, it was redesignated S₅. The genotypes of five uncharacterised self-incompatible cultivars were inferred from zymograms as follows: ‘Desmayo Largueta’ and ‘Glorieta’, S₁S₅, ‘Masbovera’, S₁S₉, ‘Tarragones’, S₂S₉, and ‘Tokyo’, S₆S₇. The alleles designated S₆ and S₉ have not previously been reported. Nine self-compatible cultivars or selections were analysed, and each showed a band corresponding to an incompatibility allele as well as a common band; however, the correspondence of this common band to S_f, the allele for self-compatibility, is unproven. This revised version was published online in July 2006 with corrections to the Cover Date.     

Plum pox virus detection in dormant plum trees by PCR and ELISA

An immunocapture polymerase chain reaction (IC-PCR) protocol and ELISA were compared for their effectiveness in detecting plum pox virus (PPV) in dormant plum material. Although the IC-PCR was about one thousand times more sensitive than ELISA, PPV was detected by ELISA in 71–80% of bark samples collected in December, January and March 1996/97 from pot-grown rootstock trees inoculated with PPV the previous March, compared with 85–86% detection in the same samples by IC-PCR. In similar samples from one-year-old shoots taken from infected branches of orchard trees, 66–81% were positive by ELISA compared with 81–87% by IC-PCR. With bulked samples taken from the fibrous roots of the pot-grown trees, PPV was detected in 92–100% of samples by IC-PCR in winter compared with only 38–65% by ELISA. These results were confirmed in samples from the roots and shoots of the same trees in 1997/98. Three samples per shoot would have been sufficient to detect PPV by ELISA in 87 of the 88 infected shoots tested during the two winters. However, infected shoots are irregularly distributed in diseased trees and PCR assays of root samples offer the potential for improving the reliability of identifying trees infected with PPV.     

Inheritance of stylar ribonucleases in cherry progenies, and reassignment of incompatibility alleles to two incompatibility groups

Stylar proteins were extracted from parents and seedlings of six progenies of cherry (Prunus avium), separated using isoelectric focusing, and the gels stained for ribonuclease activity. The zymogram of each plant showed two main ribonuclease bands in the region pI 8.3 to 9.6. Progenies from crosses of parents with one band in common segregated into just two classes, whereas progenies from crosses of parents with no common bands segregated into four classes, the two types of segregation corresponding to those expected from semi-compatible and fully-compatible crosses respectively. This behaviour was consistent either with the ribonuclease locus being tightly linked with the self-incompatibility, S, locus, or else with the S locus coding for the ribonuclease variants. Evidence favouring the latter hypothesis is discussed. An apparently anomalous segregation led us to assign to ‘Bradbourne Black’ a genotype different from that previously reported, and analysis of some other cultivars in the same incompatibility group, Group VII, led us to conclude the genotype of this group is S₃S₅, and not S₄S₅ as previously reported. Correspondingly, we suggest the genotype of Group V is S₄S₅, and not S₃S₅. Five new S alleles, S₇, S₈, S₉, S₁₀ and S₁₁ were proposed in parental cultivars and selections that had not previously been assigned a genotype. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stable gene expression in transgenic apple tree tissues and segregation of transgenes in the progeny — Preliminary evidence

Summary We report here, for the first time, the stable expression and Mendelian segregation of transgenes in a tree species. So far we have evidence for a 1 : 1 segregation of thenos gene in the R1 of transgenic apple progeny. In addition we present evidence for stable gene expression of bothnos and the co-transferred genenptII in the fruit flesh of the apple fruit some 7 years after the initial transformations.     

White rot of Panax quinquefolius caused by Sclerotinia nivalis

American ginseng (Panax quinquefolius), one of the most well-known araliaceous perennial herbs, suffered from root rots and mortality in 2020 in Taibai County, Shaanxi Province, China, leading to 40%–60% yield losses. The diseased plants initially showed unevenly yellowing foliage, and yellow-brownish, water-soaked roots with internal softening. Subsequently, white fluffy mycelia manifested on the surface of diseased P. quinquefolius roots, followed by the appearance of black irregular sclerotia-like bodies. In this study, a fungal isolate (SS-TB, GenBank no. MT830866) was obtained from the infected roots. Based on the culture morphology, pathogenicity tests and phylogenetic analysis of the internal transcribed spacer (ITS) region, this isolate was identified as Sclerotinia nivalis. The optimum temperature for mycelial growth and sclerotial production was 20 ℃ and 15 ℃, respectively; the optimum pH for mycelial growth and sclerotial production was pH 6.0. This isolate grew faster and produced more sclerotia on potato dextrose agar than on other media. It infected ginseng roots with or without wounds, but inoculation of wounded roots led to more severe disease. S. nivalis also infected 43 of the 48 plant species tested, including vegetables, fruits, oil crops, and flowering plants from Fabaceae, Asteraceae, Solanaceae, Cucurbitaceae, Brassicaceae, Apiaceae, Rosaceae, Liliaceae, Chenopodiaceae, and Orchidaceae. It was nonpathogenic on Triticum aestivum, Zea mays, Anemone vitifolia, Ipomoea batatas, and Vaccinium sp. This study is the first report of S. nivalis causing white rot on P. quinquefolius.     

Assessment of natural and induced genetic variation in Alstroemeria using random amplified polymorphic DNA (RAPD) markers

Summary We have used random amplified polymorphic DNA (RAPD) markers to study genetic variation in Alstroemeria. The first objective was to examine the discriminatory power of RAPD markers in different genotypes of Alstroemeria obtained by traditional breeding. All genotypes examined, including commercial Alstroemeria varieties, could be distinguished on the basis of their RAPD profiles. Progeny plants could be distinguished from their parents. A second objective of this study was to investigate whether RAPD markers can be used as a routine tool to detect mutant plants, as an alternative to glasshouse testing. To address this objective, we analysed Alstroemeria plants that carried phenotypically visible mutations that either were induced by irradiation using X-rays or were the result of somaclonal variation. In eight out of a total of 13 mutant Alstroemeria plants obtained after irradiation or tissue culture we detected no polymorphisms when compared to control plants that were considered to be non-mutated. Only in five of the mutant plants analysed we detected one to two polymorphisms. These results suggest that frequent genome rearrangements had not occurred in the mutant plants analysed. These results also demonstrate that the RAPD technique is an inappropriate tool for the rapid screening of Alstroemeria for induced variation. It that the RAPD technique is an inappropriate tool for the rapid screening of Alstroemeria for induced variation. It seems probable that this conclusion would be equally applicable in other plant genera in which induced variation has occurred. However, the RAPD technique is a simple and effective tool for genetic fingerprinting of Alstroemeria varieties, provided their differences are due to sexual propagation.     

Isoenzyme aided selection in the transfer of mildew (Podosphaera leucotricha) resistance fromMalus hupehensis to the cultivated apple

Summary The isoenzymic geneGOT-1 was used as an indicator of ploidy levels and hybridity in the progeny of a 4x × 2x (A878/5,GOT-1 abdn × ‘Gloster 69’,GOT-lcc) cross, derived from the apomictic species (Malus hupehensis), which segregated for mildew resistance. The distinction between resistant and susceptible plants was sharp. After 3 months in a greenhouse, resistant plants showed no signs of sporulation. Of the hybrid seedlings (diploid and triploid) 78% were mildew resistant. This analysis was facilitated through the use of theGOT-lc allele, as a marker of hybridity. It appears that the prospects of transferring high mildew resistance fromM. hupehensis to the cultivated apple are promising; of the 65 hybrid resistant seedlings 18 were diploid. A similar approach in earlier generations might have facilitated the earlier transfer of this resistance to the cultivated apple.     

Effect of Environmental Conditions on Germination and Survival of Teliospores and Basidiospores of the Pear Rust Fungus (Gymnosporangium asiaticum)

Pear rust, caused by Gymnosporangium asiaticum, is an important disease of pear (Pyrus spp.) in China in areas where cypress (Juniperus spp. and Sabina spp.), the alternate host, is present. Controlled environment experiments were conducted to study the effects of temperature, relative humidity (RH) and duration of free water on germination of teliospores and basidiospores of G. asiaticum. Teliospores, sampled from Juniperus chinensis, germinated at temperatures ranging from 5 to 28 , with an optimum between 16 and 20 . For teliospores to germinate, telial horns required free water: soaking in water for 30 sec triggered teliospore germination. After initial wetting, RH had little effect on germination of teliospores except at extreme temperatures (5 and 30 ) where germination needed near-saturation moisture. The minimum time for telial horns to produce basidiospores was about 3 h at optimum temperatures. Teliospores in all telial horns germinated at 12--4 , but at 8 and 28 only those from a third of telial horns germinated. Basidiospores germinated at 5--0 with the optimum around 15 ; they needed free water or saturated moisture to germinate. Germination in free water was about eight times greater than at 100% RH. Logistic models described well the germination dynamics of basidiospores. Basidiospore survival declined exponentially with storage time, and linearly with increasing temperature and decreasing RH. Basidiospores survived for at least six days in dry conditions with RH as low as 45%.     

The effects of constant and fluctuating temperatures on the length of the incubation period of apple powdery mildew (Podosphaera leucotricha)

The effects of constant and fluctuating temperatures on the incubation period of apple powdery mildew, caused by Podosphaera leucotricha , were studied. At constant temperatures, incubation periods ranged from 3 to 12 days over temperatures 8°C–30°C, and no visible lesions developed at 32°C. A nonlinear model was developed to describe the relationship between temperature and the rate of mildew colony development. The resulting curve is bell-shaped with an optimum temperature at about 23°C. When this model was used to predict mildew development under fluctuating temperatures at an integration step of 48 min, however, it consistently overestimated development rate for fluctuating periods with average temperatures higher than 20°C. A nonlinear model was also fitted directly to the fluctuating temperature data, thus taking into account the nonlinear effect. The overestimation of development rate by the constant model for high temperatures was confirmed when the two models were compared. This overestimation probably resulted from differences in the levels of relative humidity between constant and fluctuating temperature regimes. Possible practical use of the model is discussed.