Infected Mother Plants Research Articles

Members of the Fusarium oxysporum Complex Causing Wilt Symptoms inMedical Cannabis in Israel, Italy, and North America Comprise a Polyphyletic Assemblage.

Members of the Fusarium oxysporum complex are ubiquitous soilborne fungal pathogens causing wilt diseases in various plant hosts. Fusarium oxysporum (Fo) f. sp. cannabis was first reported causing wilt disease in hemp in Italy in 1962. To date, Fusarium wilt continues to cause concern in industrial and medicinal cannabis cultivation worldwide. During a 3-year period (2018 to 2021), Fo strains were isolated from medical cannabis plants (Cannabis sativa) exhibiting wilt symptoms that were cultivated in numerous commercial farms in Israel. A diverse set of these strains was subjected to molecular phylogenetic analyses to assess their genetic diversity and to compare them with other f. sp. cannabis isolates included in prior studies. Maximum likelihood bootstrap analysis of a partial translation elongation factor (TEF1) dataset, which included 24 f. sp. cannabis sequences, revealed that the 11 strains from Israel comprised five TEF1 haplotypes. Two of the haplotypes from Israel were identical to isolates previously reported from British Columbia and California and British Columbia and Ontario. Overall, the 24 f. sp. cannabis sequences included 12 unique TEF1 haplotypes. These were phylogenetically diverse, suggesting that pathogenicity to C. sativa may have evolved independently within the F. oxysporum complex. Pathogenicity tests of the Israeli strains were confirmed by Koch's postulates assays. Strains of the five different f. sp. cannabis TEF1 haplotypes all caused wilt in cannabis seedlings but with varying levels of aggressiveness. The same isolates that originated from asymptomatic infected mother plants were found in wilted cuttings indicating that the pathogen can be spread via propagation material.

Transmission of Fusarium oxysporum f. sp. fragariae Through Stolons in Strawberry Plants.

Fusarium wilt of strawberry, caused by the soilborne pathogen Fusarium oxysporum f. sp. fragariae, is a growing threat to the strawberry industry worldwide. Symptoms of the disease typically include stunting, wilting, crown discoloration, and eventual plant death. When Fusarium wilt was discovered in California, the disease was not known to occur anywhere else in North America. Long distance movement of the pathogen would most likely occur through transport of infected plants, which seems plausible if strawberry plants can sustain infections without showing symptoms of disease. The results of this study document that F. oxysporum f. sp. fragariae can move through stolons of infected mother plants and colonize first-generation daughter plants. The pathogen can also move through stolons from first to second-generation daughter plants. Daughter plants of both generations were always symptomless. The pathogen was recovered from both roots and petioles of infected daughter plants. Similar results were obtained for two cultivars known to be susceptible to Fusarium wilt, Albion and Monterey. Transmission through stolons from mother to daughter plants also occurred in the resistant cultivar, San Andreas, but less frequently than in Albion and Monterey.

Elimination of Indian Citrus Ringspot Virus in Kinnow by Using Phytoproteins with Shoot‐tip Grafting

The combined beneficial effect of shoot‐tip grafting with phytotherapy of different phytoproteins obtained from roots of Boerhaavia diffusa and leaves of Clerodendrum aculeatum to eliminate Indian citrus ringspot virus (ICRSV) from Kinnow is reported. The study also reports the effect of these phytoproteins on the growth and proliferation of Kinnow explants when nodal segments from infected mother plants (confirmed by RT‐PCR) cultured in MS containing different concentrations of aqueous extracts of these individual phytoproteins. Shoot‐tips from these nodal sprouts were grafted on Citrus jambhiri under in vitro condition. Phytoproteins from C. aculeatum were found utmost effective in respect of elimination of 50% virus followed by B. diffusa (40%). In respect of promotion of growth and proliferation of nodal explants, B. diffusa was found most effective followed by C. aculeatum. The plants were considered virus‐free when they showed absence of ICRSV in both DAC‐ELISA and RT‐PCR tests.Plant Tissue Cult. & Biotech. 27(1): 1-11, 2017 (June)

First Report of Grapevine rupestris stem pitting-associated virus in Wild Grapevines (Vitis vinifera spp. sylvestris) in Tunisia

Wild grapevines (Vitis vinifera spp. sylvestris) grow in the northern part of Tunisia, and can potentially be natural reservoirs of pathogens including viruses. Grapevine Rupestris stem pitting-associated virus (GRSPaV), a member of the genus Foveavirus in the family of Betaflexiviridae. It is present in grapevines worldwide and is associated with rupestris stem pitting (RSP) and grapevine vein necrosis (Meng et al. 2013). The virus has been detected in the pollen of infected grapevines (Rowhani et al. 2000), but its spread through pollen is not confirmed, although it is transmitted by seed from infected mother plants to their progeny (Lima et al. 2006b). In Tunisia, GRSPaV is very common in table grape cultivars (Soltani et al. 2013) but no data are currently available on the presence of viruses in Tunisian wild grapevines, which can play a role in the dissemination of viruses to the cultivated grapevines. To address this knowledge gap, a survey was carried out in the mountain forests of northern Tunisia...

Trichoderma atroviride SC1 prevents Phaeomoniella chlamydospora and Phaeoacremonium aleophilum infection of grapevine plants during the grafting process in nurseries

Phaeoacremonium aleophilum (Pal) and Phaeomoniella chlamydospora(Pch) are commonly and consistently found in the wood discoloration of the three tracheomycotic syndromes of esca and are thus considered the causal agents of this phaeotracheomycotic complex. Infections commonly occur in vineyards or derive from infected mother plants. However the grafting process in nurseries can pose an additional risk of infections. Trichoderma atroviride SC1, applied at the hydration, callusing and pre-planting stages, effectively controlled infection of Pal and Pch, hydration treatments proving the most effective. The viability of conidia of T. atroviride SC1 in the suspension used to soak the grapevine cuttings did not change within the first 72 h at temperatures of between 5 and 15 °C and it was possible to re-use the suspension at least four times within 48 h without losing viability, making the treatment a practical and valuable measure for nurseries.

Evaluation of Seed Transmissibility of Soybean Vein Necrosis-Associated Virus in Two Soybean Cultivars Grown Under Field Conditions

Soybean vein necrosis-associated virus (SVNaV), originally found in Tennessee in 2008, has recently been reported from other soybean-growing regions of the United States as well as Canada. To provide direct evidence for lack of seed transmissibility of SVNaV in soybean, cultivars CF386RR2y/stsn and AG4832 were planted in a field in Kentucky during the 2013 growing season. Typical SVNaV induced symptoms emerged in early August. Tissues were collected from 150 symptomatic and asymptomatic plants of both cultivars and assayed by ELISA. SVNaV was detected in 94% of symptomatic, but none of asymptomatic plants. Seeds were harvested independently from 10 selected infected plants of each cultivar that exhibited the highest ELISA readings. A total of 2085 seeds from both cultivars were planted under greenhouse conditions and subsequently 1955 asymptomatic seedlings were harvested 4-5 weeks post-emergence and assayed individually by ELISA. Sap from only one of the seedlings exhibited an absorbance reading higher than background. However, when all the seeds from the same mother plant were grown and tested, none was positive. This suggests higher than background absorbance value for this single seedling is an anomaly. To search for probable genetic variation among SVNaV isolates from infected mother plants, whose seeds were subjected to grow out test, nucleocapsid protein gene was RT-PCR amplified from 13 mother plants representing both cultivars and sequenced. The analysis of sequences revealed the presence of distinct variants. Lack of potential for SVNaV to be seed transmissible in soybean is discussed.

Spread of Xanthomonas campestris pv. musacearum in banana plants: implications for management of banana Xanthomonas wilt disease

Banana Xanthomonas wilt (BXW) caused by Xanthomonas campestris pv. musacearum (Xcm) is a devastating disease of bananas in Uganda and across the Great Lakes region of East and Central Africa. While use of disease-free suckers is recognized as important to control BXW, bacterial movement from infected mother plants to their suckers is not well understood. In this study, the movement of Xcm through the pseudostem of naturally and artificially infected bananas was examined. In naturally infected plants, samples of plant organs collected from susceptible cultivars ‘Kayinja’, ‘Nfuuka’ and Kivuuvu’ (Musa acuminata) at various stages of disease were analysed using a polymerase chain reaction assay employing Xcm specific primers. Xanthomonas campestris pv. musacearum was detected in 70% of asymptomatic corms and suckers collected from each of the three susceptible cultivars. In ‘Kayinja’ and ‘Nakitembe’, Xcm was recovered from plant parts 20 cm away from the point of inoculation prior to symptom development. The population of Xcm was variable within and among the plant parts over time, with the highest number being recorded in the inoculated region for all cultivars. No disease was observed seven days after inoculation of the Xcm-resistant wild species M. balbisiana and Xcm was restricted to the point of inoculation. This study implies that by the time wilt symptoms are expressed, Xcm has migrated from the point of entry to most parts of the plants. Use of suckers from infected plants should be restricted as they are likely to be latently infected and could thus result in disease when transplanted.

First Report of Impatiens necrotic spot virus (INSV) Infecting Basil (Ocimum basilicum) in the United States.

Basil (Ocimum basilicum L.), a native of India belonging to the Lamiaceae family, is an aromatic herb with distinctive aroma, and several commercial varieties are used extensively for culinary and ornamental purposes. During the summer of 2011 and 2012, potted plants of basil in a commercial greenhouse in the Richland-Kennewick area of Washington State were observed showing foliar symptoms consisting of chlorotic spots, ring spots, leaf distortion, and stem necrosis. In initial tests, extracts of symptomatic leaves were positive for Impatiens necrotic spot virus (INSV; genus Tospovirus, family Bunyaviridae), when tested with INSV immnunostrips (Agdia, Inc., Elkhart, IN). These samples were negative with immunostrips specific to Tomato spotted wilt virus (genus Tospovirus) and group-specific potyviruses. The virus from symptomatic leaves of basil was transmitted by leaf rub inoculation to Nicotiana benthamiana and Emilia sonchifolia, where it produced necrosis on inoculated leaves followed by systemic necrosis in the former and chlorotic spots and mosaic mottling in newly developed leaves in the latter. Symptomatic leaves from both host plants tested positive with INSV, but not with TSWV, immunostrips. For additional confirmation of INSV, total RNA was extracted from symptomatic leaves of basil using RNeasy Plant Minikit (Qiagen, Inc., Valencia, CA) and used for reverse transcription (RT)-PCR amplification of the nucleocapsid (N) gene using forward (5'-AGCTTAAATCAATAGTAGCA-3') and reverse (5'-AGCTTCCTCAAGAATAGGCA-3') primers. RT was carried out at 52°C for 60 min followed by denaturation at 94°C for 3 min. Subsequently, 35 cycles of PCR was carried out with each cycle consisting of 94°C for 1 min, 58°C for 45 s, and 72°C for 1 min, followed by a final extension step at 72°C for 10 min. The amplicons of about 610 nt obtained from RT-PCR were cloned into pTOPO2.1 vector (Invitrogen Corporation, Carlsbad, CA) and three independent clones were sequenced in both directions. Sequence analyses of these clones (GenBank Accession No. KC218475) showed 100% nucleotide sequence identity among themselves and 99% nucleotide sequence identity with INSV isolates from the United States (DQ523598, JX138531, and D00914) and a basil isolate (JQ724132) from Austria. These results further confirm the presence of INSV in symptomatic leaves of basil. Previously, basil has been reported to be naturally infected with TSWV in the United States (3) and INSV in Austria (2). Therefore, this study represents the first confirmed report of the virus in basil in the United States. No species of thrips vector was observed on the affected basil plants. The discovery of INSV in basil has important implications for the nursery industry due to the broad host range of the virus (1); stock plants may serve as a source of inoculum in production areas and infected plants could be distributed to homeowners. It is important for commercial nurseries to monitor for INSV to identify infected mother plants to prevent virus spread. Since more than 31 viruses belonging to 13 different genera have been reported in basil ( http://pvo.bio-mirror.cn/famly073.htm#Ocimumbasilicum ), further studies are in progress to determine if the observed symptoms on basil are only due to single infection of INSV.

Occurrence of Phaeomoniella chlamydospora on grapevine planting material in Sardinia and its control with combined hot water and cyproconazole treatment.

The occurrence of Phaeomoniella chlamydospora was investigated during the propagation process of an Italian nursery, and combined hot water and cyproconazole treatments were carried out to limit its spread in nursery plants. In the three–year period 2005–07, cutting and graft samples (scion cv Sangiovese, rootstock cvs 140Ru in 2005 and 1103P in 2006–07) were taken during the propagation process at several infection risk stages in order to assess the presence of P. chlamydospora. Moreover, in 2005 and 2006 cuttings from esca–symptomatic grapevines (scion cv Sauvignon blanc, rootstock cvs 140Ru in 2005 and 1103P in 2006) were treated at different stages of the propagation process. In 2007, artificially infected 1103P cuttings were treated after inoculation with P. chlamydospora (107 conidia ml-1). Cuttings and callused graftlings were treated by dipping in a hot water bath at 50°C for 30 min (HWT) or in a cyproconazole suspension (0,1 g a.i. l-1) for at least 12 h, in different combinations. At each stage of infection risk and at each treatment woody material was collected and grown in pot, avoiding accidental contamination, or in the field nursery for one season and then destructively examined. DNA was extracted from wood collected at different points along the plant and analysed by nested PCR with Pch-specific primers. One-mm thick woody slices from artificially inoculated cuttings were plated on MEA plus antibiotics and fungicides. Despite the extended wood discoloration, P. chlamydospora occurrence on nursery plants was scarce in the three–year period. Planting material contamination may have resulted from infected mother plants (from 0.0 to 6.7 % of infected cuttings were obtained directly from non-symptomatic mother plants) or from the propagation process, particularly during the stages following grafting (0.0 to 23.3 % of infected grafts). Canes from esca–diseased mother plants were always contaminated, but in quite different percentages (about 30 % of the cuttings examined in 2005, from 1.9 to 4.1 % in 2006 and 2007). However, no final conclusion could be drawn about which stages played a major role in the contamination of nursery plants, due to the low and irregular infection frequencies detected in the propagation process. As regards P. chlamydospora control, HWT performed on cuttings before or after cold storage influenced vegetative growth depending on both the cultivar and the growth conditions, but it was deleterious on callused graftlings. Natural contamination on nursery material in 2005 and 2006 was insufficient to assess the effectiveness of treatments. In 2007, HWT and cyproconzole treatments alone were not effective in reducing the percentage of infection in cuttings that were artificially inoculated. Only cyproconazole immediately followed by HWT significantly reduced the number of infected cuttings, but it was not sufficient to eradicate the pathogen.

Visual inspections of nursery stock fail to protect new plantings from Blueberry scorch virus infection

Blueberry scorch virus (BlScV) is one of the most pervasive pathogens of highbush blueberry. The virus is aphid-vectored and exhibits a latent period between infection and symptom expression in the host plant of up to 5 years. In many cases, we have observed BlScV symptom expression in new fields that appears inconsistent with aphid-vectored introduction and spread. It was, therefore, speculated that the virus may be introduced through infected nursery stock. To examine this possibility, we first surveyed selected nurseries to determine if mother plants, used for propagation by cuttings, were BlScV-infected. Two nurseries were found to harbor symptomless, infected, mother plants (cv. Duke). Cuttings from one nursery were collected from infected and non-infected plants and rooted in propagation beds. The survival and infection of cohorts from each mother plant were determined one year after planting. A significantly greater proportion of cuttings survived from non-infected mother plants (0.7) than from infected mother plants (0.5). Of the cohort from infected mother plants that survived, 40% tested positive for BlScV. We also surveyed the distribution of infected, symptomatic plants in recent ‘Duke’ plantings that originated from nurseries with BlScV-infected mother plants and compared distribution with older plantings with more advanced BlScV outbreaks. In all cases, the distribution of BlScV symptom development in young fields was random, which is consistent with introduction from planting stock. Older plantings showed a strong clustered distribution, which is consistent with aphid transmission. This study identifies infected nursery stock as an important source of BlScV dissemination and underscores the importance of having symptomless mother plants virus tested.

Serological detection of seed borne viruses in cowpea regenerated germplasm using protein a sandwich enzyme linked immunorsorbent assay

Cowpea (Vigna unguiculata (L.) Walp) is susceptible to a number of fungal, bacterial and viral diseases. The effects of viruses can be devastating and are a major constraint to the production of cowpea. A study was carried out to detect the presence of seed borne viruses in fourteen cowpea accessions screened from 300 regeneratedcowpea germplasm from the genebank collection of the International Institute of Tropical Agriculture (IITA) in Nigeria. Protein A Sandwich Enzyme linked Immunosorbent Assay (PAS ELISA) was used to detect seed borne viruses in the accessions. Out of 36 accessions of TVu 033 indexed, 31 were infected with Cowpea aphid-borne mosaic virus genus Potyvirus, which is of great economic importance in germplasm conservation and exchange between countries as it causes great loss. Southern bean mosaic virus was not detected in any of the accessionsevaluated. Seeds were harvested from the infected mother plants at maturity and the embryos excised in vitro onto hormone free medium composed of 4.43 g MS basal salt, 30 g sucrose and 8 g of agar. The seedlings obtained were serologically indexed to detect any seed-borne viruses after acclimatisation to screen house conditions. Theseedlings obtained from excised embryos got from harvested seeds gave a negative ELISA result.

First Report of Potato spindle tuber viroid in Cape Gooseberry (Physalis peruviana) from Turkey and Germany.

Since the recent identification of Potato spindle tuber viroid (PSTVd) in vegetatively propagated ornamental plant species (4), many growers have asked to have their mother plants tested for this viroid. In December of 2007, a grower from Turkey submitted cuttings of cape gooseberry (Physalis peruviana) to be tested for PSTVd. Initial testing by real-time reverse transcription (RT)-PCR according to Boonham et al. (1) indicated the presence of either Mexican papita viroid, PSTVd, or Tomato chlorotic dwarf viroid in four samples. To identify the viroid(s) present, isolated RNA from these samples was used for RT-PCR (2), and products of the expected full genome size for the three viroids were amplified from each sample. One of the PCR products was sequenced (GenBank Accession No. EU862230) and analysis of the 357 nt sequence indicated it was most related to PSTVd sequences belonging to the so-called 'Oceanian' strain of the viroid (3), with 99.7% identity to GenBank Accession No. AY962324. Therefore, the viroid was identified as PSTVd. Pathogenicity of this PSTVd genotype was demonstrated when 4 weeks after mechanical inoculation with sap extracts seedlings of tomato cv. Money-maker showed the expected viroid symptoms of chlorosis and stunting, and the presence of the viroid in these plants was confirmed by RT-PCR (2). In March of 2008, by use of RT-PCR (2) and sequencing of the PCR product (GenBank Accession No. EU862231), PSTVd was identified in young seedlings of P. peruviana from a German grower. The German isolate differed at only three nucleotide positions from the Turkish isolate. The identification of PSTVd in young seedlings indicates that seeds had been source of infection, whereas in the case of the PSTVd infected cuttings from Turkey, the infection originated from infected mother plants. To our knowledge, these are the first reports of PSTVd in P. peruviana. Although infected P. peruviana plants did not show symptoms, they might act as sources of inoculum for crops like potato and tomato, which may suffer serious damage.

The Use of Thermotherapy and in vitro Meristem Culture to Produce Virus-Free ‘Chancellor’ Grapevines

ABSTRACT Grapevines (Vitisspp.) are very susceptible to virus diseases. Virus infection reduces fruit yield and quality. The objective of this work was to determine the usefulness of thermotherapy (37.2°C) and in vitromeristem culture to obtain virus-free grapevine plants cv. ‘Chancellor’. Grapevine leafroll-associated virus 1,3(GLRaV-1, 3) infected grapevines were multiplied in vitrofrom two infected mother-plants in half strength Murashige and Skoog medium (1/2MS) supplemented with 0.5 mg/L of BA and the in vitroplants were initially tested by ELISA to confirm their virus status; subsequently, 96 infected in vitroplants were propagated on 1/2MS medium with BA and subjected to 0, 7, 10, 12, 14, 16, 18, 20 or 22 days of exposure at 37.2°C. Afterward, the apical meristems from the plants surviving the thermotherapy treatment were excised and transferred to fresh 1/2MS medium with 0.5 mg/L of BA and grown in a culture room until they developed into entire plants. Control plants and all the plants that survived thermotherapy were assessed for their virus status using both ELISA and RT-PCR. After 20 days of exposure at 37.2°C, 100% of the plants submitted to thermotherapy were found to be virus-free by RT-PCR and ELISA tests. Plants derived from meristems with two or three primordial leaves remained virus infected. However, when meristem culture was combined with thermotherapy (12 or more days of heat treatment), all the meristem-derived plants were virus-free.

NON-TRANSMISSION OF PLUM POX VIRUS

The vertical transmission of Plum pox virus (PPV) from infected mother plants to their progeny has been investigated for many years with controversial reports. The first investigations about PPV transmission through seeds were based only on biological tests: Szirmai (1961) recorded seed transmission in apricot, Savulescu and Macovei (1965) and Coman and Cociu (1976) in plum and peach, while Jordovic (1963) were not able to detect PPV in plum seedlings. Despite of serological and molecular diagnosis development, reports about vertical transmission of PPV revealed different results. Nemeth and Kolber (1982) detected in apricot seedlings a low transmission rate of PPV while Shimanski et al. (1988) in plum and apricot, Eynard et al. (1991) and Triolo et al. (1993) in apricot found no transmission of PPV in seedlings from infected seeds. Pasquini (1998, 2000) obtained negative results regarding vertical transmission on 12 apricot cvs. infected with D strain and six peach cvs. infected with M strain. The same results were obtained by Myrta et al. in apricot and plum (1998) and Glasa et al. in plum and myrobolan (1999). Slovakova et al. (2002) reported the transmission of PPV in a few seedlings from infected seeds using DAS-ELISA. Recently study of Milusheva et al. (2008) showed non-transmission through seeds of PPV-M strain in plum and PPV-Rec strain in apricot.

In vitro production of Indian citrus ringspot virus (ICRSV) free Kinnow plants employing thermotherapy coupled with shoot tip grafting

Indian citrus ringspot virus (ICRSV) is known to cause serious disease problem in Kinnow (Citrus nobilis Lour × C. deliciosa Tenora) plants. This work reports the elimination of ICRSV by using thermotherapy coupled with shoot tip grafting in vitro. Nodal segments from infected mother plants (indexed by indirect ELISA and RT-PCR) were treated both in water bath and moist hot air at different temperatures viz. 40, 45 and 50°C for 30, 60 and 120 min and cultured on MS medium containing 2-iP (1 mg/l) and malt extract (800 mg/l). Shoot tips were excised from the nodal sprouts and grafted on to rough lemon (C. jambhiri) rootstock under aseptic conditions. Water bath treatment was found to be more effective as compared to moist hot air treatment as maximum number of ICRSV free plants (36.84%) were obtained by grafting the tips (0.7 mm) taken from the nodal segments treated at 50°C in water bath for 2 h. In an alternate treatment regime, 1-year-old infected plants were kept at various temperatures viz.36, 38 and 40°C in a thermotherapy chamber. Maximum of 60% ICRSV free plants were obtained by grafting the tips (0.7 mm) from the plants placed at 40°C followed by the plants placed at 38°C (59.09%) and the least was observed in case of the plants placed at 36°C (40.74%). Only those plants/plantlets were considered virus free, which showed negative reaction both in Indirect ELISA and RT-PCR.

The question of seed transmissibility of Plum pox virus

For many years, Plum pox virus (PPV) was considered to be transmissible by seed, increasing the fear of long‐distance spread of the disease. In the late 1970s, it was claimed on the basis of biological transmission of the virus to herbaceous indicator plants and the development of serological diagnosis based on polyclonal antibodies, that PPV was seed‐transmitted, with a different infection rate according to the plant species and part of the seed which was tested. In the 1990s, PPV was characterized into four different types, and specific monoclonal antibodies were produced for them. These new and more sensitive diagnostic techniques, together with RT‐PCR with different sets of specific primers, were used to approach once again the problem of PPV transmission through seeds. The virus was detected in seed coats and cotyledons, but embryonic tissue and seedlings obtained from germinated seeds never showed symptoms, and gave negative results for PPV with both ELISA and PCR assays. No PPV isolate is currently recognized to be seed transmitted, so vertical transmission of PPV from infected mother plants to their progeny does not occur. Hypothetically, the only possibility of seed transmission would arise from a mutation in the helper component of the virus, associated with high susceptibility of the infected Prunus cultivar.

Effect of a multispecies nematode population on the root, corm, and shoot growth of East African Musa genotypes

A study to determine the impact of a multispecies nematode population on the root, corm, and shoot growth of East African Musa genotypes was carried out. Eight genotypes comprising the plantain “Gonja” (Musa AAB group), the dessert banana “Sukali Ndizi” (AAB), the beer banana “Kayinja” (ABB), and five East African Highland bananas (AAA-EA) were assessed at flower emergence of the plant crop. Root damage and plant growth characteristics were assessed on both infected and noninfected plants. This study showed that Radopholus similis and Helicotylenchus multicinctus were recovered in highest numbers from infected mother plants. Significantly (P<0.05) higher shoot and root damage was observed in the infested plot compared to the noninfested plot. The differences in nematode damage observed among the different Musa genotypes confirm the variability in susceptibility to nematodes. Most of the East African Highland bananas and “Gonja” had a significant reduction in root system size. In addition, toppling and lengthening of the period to flower emergence of the plant crop was much more pronounced in these genotypes. In contrast to previous reports, this study indicated that a multispecies nematode infection significantly (P<0.05) reduced shoot and root growth of “Kayinja”. “Sukali Ndizi”, however, was observed to be tolerant to nematode infection as a small reduction in the root system size was associated with a negligible effect on the corm and shoot growth characteristics. Therefore, the percentage reduction in root and shoot growth due to nematode infection is not constant but depends on the plant genotype.

Effects of high vineyard temperatures on the grapevine leafroll associated virus elimination from Vitis vinifera L. cv. Napoleon tissue cultures

In vitro culture of shoot tips and axillary buds was used for virus elimination from the Spanish autochthonous table grapevine cultivar Napoleon which was infected by Grapevine leafroll associated virus-3 (GLRaV-3) and Grapevine fanleaf virus (GFLV). High percentages of GLRaV-3-free plants (91–100%) were obtained by establishing shoot tip cultures from infected mother plants of the 29-228, 74-16 and 77-266 clones. Lower percentages of virus-free plants (71–87%) were obtained by in vitro culture of the first, the second and the third axillary buds of the growing distal shoots. Percentages of virus-free plants obtained with both shoot tips and axillary buds varied according to the time of the year when the explants were collected and the bud position on the shoot. A increased efficiency of in vitro tissue culture methods was observed when cultures were established in summer and it was due in part to the high vineyard temperatures reached in the southeast of Spain during the hot season. GFLV- and GLRaV-3-free plants were only obtained by thermotherapy in combination with tissue culture methods from co-infected plants of the clone 39-29.

Differential Infection of Mother and Runner Plant Generations by Verticillium dahliae in a High Elevation Strawberry Nursery

Strawberry cultivars Selva and Camarosa (Fragaria ×ananassa Duch.) were grown at a high elevation nursery in soil that was either naturally infested with Verticillium dahliae or was rendered pathogen-free through preplant fumigation with 2 methyl bromide: 1 chloropicrin (wt/wt) at 392 kg·ha-1. Plants grown in fumigated soil were inoculated with a conidial suspension of V. dahliae, prior to establishment. Just prior to harvest, plants were rated for disease based on symptoms of Verticillium wilt. At the same time, petiole samples were taken from mother plants and each of three generations of runner plants, along with the stolons subtending each of the sampled runner plants. Petioles and stolons were cultured to assay for the presence of V. dahliae, and scored as either infected or not infected. The experiment was conducted in each of two successive years, and the following conclusions were supported by results obtained in both years. First, symptoms of Verticillium wilt on mother plants of both cultivars were highly correlated with recovery of V. dahliae from petioles, but runner plants were consistently free of symptoms even though they were often infected. Second, runner plants sustained lower infection frequencies than mother plants, with the differences being significant in most cases. Lastly, infection of runner plants was due, at least in part, to transfer of inoculum from infected mother plants; in some cases this appears to have been the exclusive mode of infection.

Chrysanthemum stunt pospiviroid

Chrysanthemum stunt pospiviroid