Factors affecting shoot development in apically dominant Acer cultivars in vitro.

Summary

Axillary shoot cultures of both Acer saccharinum L. ‘Pyramidale’ and A. platanoides L. ‘Crimson King’ displayed strong apical dominance and prolific basal callus in vitro, which was not conducive to rapid multiplication and rooting. Basal callus was reduced in ‘Pyramidale’ by replacing 6-benzylaminopurine (BAP-5μM) with zeatin (5μM), but this also reduced axillary shoot growth. The addition of 2,3,5-triiodobenzoic acid (1-20 μM) altered callus development and promoted a concentration-dependent increase in axillary shoot growth. Supplementing medium with thidiazuron (0.005 and 0.05 μM) in addition to BAP (1 μM) enhanced shoot growth, especially with nodal shoot sections, and increased subsequent rooting. Although thidiazuron also increased basal callus, this correlated with better shoot growth in ‘Crimson King’. Selection of apical buds from ‘Crimsom King’ stockplants was essential for the establishment of sustainable cultures; axillary bud-derived expiants quickly died. Once shoots of ‘Pyramidale’ and ‘Crimson King’ had elongated, they could be readily rooted in vitro, and plantlets were successfully weaned under high humidity ‘dry fog’.     

Root formation,bud growth and survival of ornamental shrubs propagated by cuttings on different planting dates

Summary

Semi-hardwood cuttings of Cornus alba ‘Sibirica’, Deutzia ‘Mont Rose’, Forsythia × intermedia ‘Lynwood’, Ligustrum vulgare ‘Liga’, Philadelphus × virginalis, Potentilla fruticosa ‘Goldfinger’, and Spiraea × vanhouttei were planted on seven dates from July to October in two years and at three locations to investigate the effect of planting date on root formation, axillary bud growth, and plant survival. Cuttings were planted directly in the field and covered with polyethylene. Generally, root formation, bud growth, and plant survival were similar both years and at the three locations. All species except Deutzia had relatively constant rooting percentages at planting dates until mid August. For all species rooting percentages declined from mid August to October. Except for Deutzia, plant survival the following spring was constant or decreasing with planting date. For all species except Potentilla axillary bud growth and survival of cuttings planted in late September or October tended to increase while rooting percentages continued to decrease. In all species there was a close relationship between axillary bud growth and survival. Results revealed that many roots per cutting accelerated axillary bud growth.     

Endogenous hormone concentrations and bud-break response to exogenous benzyl adenine in shoots of apple trees with two growth habits grown on three rootstocks

Summary

Scions from two siblings of a ‘Goldspur Delicious’ × ‘Redspur Delicious’ cross were budded to three rootstocks with different levels of vigour [M.9, M.7, and Malus domestica ‘Antanovka’ seedling] and planted in the field in 1997. The scions had two contrasting growth habits: one with narrow crotch angles, numerous short branches and an upright narrow (UN) canopy; and the other with wide crotch angles, few short branches, and a spreading round (SR) canopy. Shoot tips were collected at the time of bud-break in April 2004 and analysed for auxin (AUX), cytokinins (CK), and abscisic acid (ABA) to determine relationships between scion growth habit, size-controlling rootstock, and shoot tip hormone concentrations. Although not statistically different, the UN growth habit had numerically higher AUX, lower ABA, and equivalent CK levels as the SR growth habit. These differences resulted in statistically higher AUX:CK ratios (ACR). It is possible that the higher ACR contributed to the UN growth habit, which had more anti-gravitrophic shoot growth and appeared to have greater apical dominance than the SR growth habit. Either growth habit, grown on seedling rootstock, had nearly twice the ACR than on M.7 or M.9 rootstocks. The synthetic CK, 6-benzyl adenine (BA), was applied to 30 cm shoot explants of both growth habits in a greenhouse in March 2006. An 8.7 mM BA concentration stimulated bud-break in both growth habits, compared with controls, and bud-break was increased more in the UN than the SR growth habit. The results indicate that the ACR may be a factor regulating bud-break and the development of growth habit in apple scions, and that rootstock modified the hormone concentrations in shoot tips.     

Effect of agar,galactomannan and indole-butyric acid on in vitro rooting of the pear cultivar ‘Durondeau’ and apple rootstock cultivar ‘Marubakaido’

Summary

The influence of partial substitution of agar by galactomannans in culture media supplemented with different concentrations of indole-3-butyric acid (IBA) was studied on in vitro rooting of pear (Pyrus communis L.) cultivar ‘Durondeau’ and apple rootstock (Malus prunifolia Borkh.) cultivar ‘Marubakaido’. The galactomannans applied were obtained from Cassia fastuosa (cassia) and Cyamopsis tetragonolobus (guar gum) seeds. The results obtained with mixtures of agar and galactomannan (3 g l^–1 each) were compared with those from media solidified with a standard concentration of agar (6 g l^–1). The rooting of pear shoots was enhanced significantly in the presence of a mixture of agar plus cassia galactomannan compared to medium solidified with agar only. The modified media promoted a higher number of roots than the control, and increased the percentage of rooted shoots. A maximum of 84.8% rooting was obtained on half-strength MS medium (¹?2MS) supplemented with 0.49 µM IBA and solidified with a blend of agar plus cassia galactomannan. For the apple rootstock, only the number of roots per shoot was influenced significantly by the addition of galactomannan to the rooting medium. The highest number of roots per shoot was 16.67 on ¹?2MS medium gelled with a mixture of agar plus guar galactomannan supplemented with 4.90 µM IBA. The behaviour of the agar-galactomannan gel and the possibility of reduced costs when compared with systems containing only agar, suggest new biological and commercial applications for galactomannans.     

In vitro plantlet regeneration from protocorms of Dendrobium lituiflorum Lindl. and Cymbidium bicolor Lindl. and their acclimatisation: effect of salts,sucrose, and banana extract

Summary

The salts present in modified Knudson C (KC) medium (1946), 2% (w/v) sucrose, and a natural banana extract (BE) [1 – 20% (v/v)] were studied singly, or in combination, for their effects on the regeneration of protocorms of the orchid species, Dendrobium lituiflorum and Cymbidium bicolor. The incorporation of KC salts along with higher percentages of BE [10% or 20% (v/v)] promoted protocorm development as well as shoot and root formation. The presence of 2% (w/v) sucrose in the medium further enhanced root lengths and the rooting percentage, irrespective of the presence of KC salts. Incorporation of both KC salts and 2% (w/v) sucrose was found to be obligatory, in conjunction with BE (a cost-effective natural additive) for plantlet regeneration. In vitro-raised plantlets of both orchid species exhibited high rates of survival under greenhouse conditions. Scanning electron microscopy revealed elliptical stomata and epicuticular granular wax deposits on their abaxial leaf surfaces after acclimatisation.     

Effects of Trichoderma harzianum strain T-22 on the growth of two Prunus rootstocks during the rooting phase

Summary

Trichoderma harzianum strain T-22 (T22) is one of the most effective strains of this fungus that is able to colonise the roots of most plant species across a wide range of soil types. This fungus is used as a biocontrol agent during crop production, and for the improvement of the rooting and acclimatisation phases in plant nurseries. In vitro-cultured shoots of GiSeLa6^® (Prunus cerasus P. canescens) and of GF677 (P. amygdalus P. persica), two important Prunus varieties used as commercial rootstocks, were inoculated with T22. The results showed that early inoculation of the fungus (at the stage of shoot transfer to root-inducing medium) seriously damaged both GiSeLa6^® and GF677 plants; whereas, following later inoculation (7 d after shoot transfer to root-inducing medium), the plants survived and showed significant increases in shoot growth and root development. In particular, root lengths in GiSeLa6^® and GF677 plants increased by 180% and 136%, respectively, compared to non-inoculated controls. Microscopic analysis revealed T22 hyphae spreading on the root surface in GiSeLa6^® (fungus colonisation frequency = 20%), but not in GF677 roots. Our results demonstrate that the application of T22 during the rooting phase resulted in greater shoot lengths, as well as increased numbers of leaves, roots, and stem diameters. These morphological characteristics could increase the quality and viability of nursery planting material and provide advantages during the plant acclimatisation phase.     

Partitioning sources of rooting potential in plum hardwood cuttings

SUMMARY

Rooting of leafless winter hardwood cuttings of the plum rootstock Prunus insititia ‘Pixy’ increased as the location from which the shoots were taken from within specially grown stockplants decreased in height above ground, associated with a parallel reduction in shoot thickness. However, the actual height of the least-ready-rooting crown cuttings had no effect on rooting, suggesting that relative rather than absolute position is important. Rooting was unaffected by bark-ringing and trunk incision distal to the shoot position, suggesting that such treatments did not interfere with a basipetally translocated root promotor which might have accounted for improved rooting of cuttings in the lower parts of the hedge. The rooting of crown cuttings above a bark ring was reduced considerably compared with that of cuttings from normal bushes, and this was associated with increased thickness of shoots distal to the ring. Delaying pruning in spring until after growth had started resulted in thinner crown shoots compared with those from plants pruned normally while dormant, and the rooting of these thinner crown shoots was much higher than that of the normal crown cuttings. It was shown by covariance analysis that shoot thickness accounted for part of the rooting response but could not account for the total effect due to shoot position within the bush, ringing, or time of pruning. Competence to root appears to develop independently in individual shoots, modified by a shoot thickness factor which favours the subordinate shoots induced in the shoot hierarchy of severely pruned hedges.     

Induction of roots on jujube softwood cuttings using Agrobacterium rhizogenes

Summary

Cuttings from trees of jujube (Ziziphus jujuba Mill.), particularly mature ones, root with great difficulty. A greenhouse experiment assessed the effects of two strains of Agrobacterium rhizogenes (A4 and TR105) on softwood cuttings from two sources: ten year old trees of cv. Li and a tree approximately 40 years old of the cv. Contorta. The cuttings were collected and trimmed to 7.5 cm. Ten weeks after inoculation, both strain and source of cutting influenced visible symptoms of infection. Jujube cuttings were more responsive to TR105 than to A4, and the ‘Li’ cuttings were more responsive than ‘Contorta’ cuttings. Strain TR105 was very effective in increasing rooting percentages and root number. ‘Li’ cuttings had better rooting percentages, greater root number, and greater root length than did the ‘Contorta’ cuttings. Inoculation with A. rhizogenes may also possess great potential for promoting adventitious root formation in other difficult woody ornamental or fruit tree species.     

Asexual Propagation of Grapevine Transmits Pierce’s Disease Pathogen (Xylella fastidiosa) to Rooted Cuttings

An objective of this study was to investigate rooting success of grape cuttings propagated from vines symptomatic of Pierce’s disease. Additional objectives were to assess if rooted cuttings could survive and produce viable plants, and determine if Xylella fastidiosa (causal agent of Pierce’s disease) could be found in rooted cuttings. In Jan. 2008, cuttings were taken from symptomatic and asymptomatic ‘Merlot’ and ‘Cabernet Sauvignon’ grapevines growing in the Hill Country and Gulf Coast regions of Texas. Six weeks after cuttings were propagated, each cutting was uprooted and evaluated for rooting and infection parameters. Cuttings were then planted in containers and held in the greenhouse to evaluate survivability. To confirm the presence of X. fastidiosa, propagated cuttings were tested by real-time polymerase chain reaction. Data indicate several rooted cuttings tested positive for X. fastidiosa and appeared viable and healthy. Therefore, vines infected with X. fastidiosa have the ability to produce asexually propagated cuttings, and potentially contaminate non-infected vineyards.     

Progress towards clonal propagation of Camellia japonica cv. Alba Plena by tissue culture techniques

Summary

Optimal rooting conditions have been determined for shoot cultures of Camellia japonica cv. Alba Plena derived from a 50 year old tree: dipping the base of shoots in 1 g l^?l solution for 15 min, followed by 12 days’ darkness, induced 87% rooting in shoots cultured with Woody Plant Medium (WPM) macronutrients. Halving the auxin concentration or exposure time considerably reduced this rate, and root formation was severely inhibited if an initial dark period for the entire shoot was not used. The type of support (agar or paper bridges) did not significantly affect the rooting percentage or number of roots per rooted shoot, but liquid media induced greater root elongation. No significant differences were observed between the use of WPM and a modified Heller’s medium as regards the rooting percentages achieved, but the number of roots formed was considerably greater with WPM, as was the survival rate after transfer to soil (70% for transfer as against 35% with the modified Heller’s medium). Best survival rates were achieved when shoots were transferred to the acclimatization soil 12 days after auxin treatment, i.e. immediately after the dark period.     

Selection-pressure effects of medium pH during regeneration on successive performances of leaf-derived Tomuri’ and ‘Hayward’ kiwifruit (Actinidia deliciosa) somaclones cultured on proliferation culture media with variable pH

Summary

The aims of the work were in vitro selecting for tolerance to high culture pH (CpH) in kiwifruit and evaluating the effects of selection pressure exerted by pH variations during regeneration. Leaf-derived ‘Tomuri’ and ‘Hayward’ kiwifruit (Actinidia deliciosa) somaclones, which had been regenerated at pH 5.7, 7 and 7.5, were compared to each other and to controls (i.e. cultures derived from ‘Tomuri’ and ‘Hayward’ mother plants through standard micropropagation techniques) for shoot growth, proliferation and appearance when cultured at up to pH 8. The proliferation rate (PR), the number of nodes (NN) produced by each shoot and axillary shoot length (ASL) decreased in all ‘Tomuri’ and ‘Hayward’ somaclones and in controls as culture pH increased. At CpH 8, ‘Tomuri’ somaclones regenerated at pH 7.0 generally tended to have higher average PR and NN than the other somaclones and control; their ASL also exceeded that of the other somaclones and was just slightly higher than in control. Regardless of CpH, ‘Hayward’ somaclone 7.5-1 tended to have higher PR, NN and ASL than other female somaclones. When shoot growth and appearance (tissue hyperhydricity, leaf yellowing or browning) were considered together through a multivariate data analysis, most ‘Tomuri’ and ‘Hayward’ somaclones which appeared less sensitive than controls to high CpH had been regenerated at pH 7 and 7.5. These regeneration and culture methods, especially the selection pressure exerted by the high pH during regeneration, thus seem to be effective in obtaining ‘Tomuri’ and ‘Hayward’ variants tolerant to high culture pH.     

The effect of split-root salinity stress on tomato leaf expansion,fruit yield and quality

Summary

A crop-scale experiment between March and October 2000 investigated the effects of split-root salinity stress and rooting volume on the expansion of leaves, fruit yield and quality in two standard round fruited cultivars of tomato (Lycopersicon esculentumMill) Solairo and Espero, grown in rockwool. To implement the treatments, a split-root method was utilized whereby different levels of salinity (expressed as EC), adjusted by the addition of NaCl, was administered to two halves of a root system. The split-root high EC (2.8/8.0 dS m^–1) treatment enhanced fruit quality by increasing the concentrations of sugar, acid, total soluble solids and reducing the incidence of visual defects such as uneven ripening and gold-spot. Split-root high EC did however reduce leaf area that corresponded with low K concentration in the leaf tissue. The split-root method utilized doubled the rooting volume compared with the standard single rockwool slab, but this extra rooting capacity had no detectable effect on leaf expansion, yield or fruit quality. Although there was little impact on yield for ten weeks after the imposition of the high EC split-root treatment, mean reductions in weekly yield occurred thereafter and were of the order of 9 and 13% for ‘Solairo’ and ‘Espero’ respectively through to the end of the experiment. The fall in yield was due, in part, to a decrease in fruit size. Whilst water uptake was reduced it was unclear how the effects on leaf growth and fruit yield were mediated in the shoot. Possible processes that coordinate responses to root-zone salinity stress are discussed. The potential use of the split-root system in commercial production is considered.     

Influence of rootstock on vegetative growth,fruit yield and quality in ‘Cuore di Bue’, an heirloom tomato

Summary

Heirloom tomatoes (Solanum lycopersicum L.) such as ‘Cuore di Bue’ are highly appreciated by consumers for their outstanding quality and flavour. Nowadays, they are often grafted onto vigorous rootstocks in order to overcome several soil-borne diseases. The present study was conducted in 2007 and 2008 in Southern Italy. Plants of ‘Cuore di Bue’, an heirloom ‘oxheart’ tomato, were grown in a greenhouse either as non-grafted plants, or grafted onto two inter-specific (S. lycopersicum S. habrochaites) rootstocks (‘Beaufort F₁’ and ‘Maxifort F₁’) in order to evaluate their effects on vegetative growth, marketable yield, fruit quality, and the sensory properties of ‘Cuore di Bue’ tomato fruit. Growth analysis revealed that ‘Maxifort F₁’ enhanced plant growth, particularly in terms of leaf area and leaf fresh weight. Grafted plants had higher leaf area ratios (by 13%) and higher leaf dry weight fractions (by 18%) compared to non-grafted ‘Cuore di Bue’ plants. Marketable yields increased by 20 – 25% in grafted plants in both years. However, total soluble solids (TSS) contents, titratable acidity (TA), and TSS/TA ratios were not significantly affected by grafting.Vitamin C contents decreased by 14 – 20% in both years in the fruit of plants grafted onto either rootstock. The sensory profiles of fruit were not modified by grafting, although taste panelists expressed a higher preference for purchasing fruit from plants grafted onto ‘Maxifort F₁’. These results confirm that, when using the appropriate rootstock/scion combination, grafting can improve plant growth and the marketable yield of heirloom tomato fruit without reducing the sensory quality of the fruit or its biochemical parameters. However, grafting can reduce vitamin C contents and, thus, nutritional quality.     

Effects of pruning intensity on the biochemical status of shoot buds in three mango (Mangifera indica L.) cultivars planted at high density

Summary

Mango (Mangifera indica L.) trees grown at high density show a decline in flowering and fruiting after good fruiting years as a result of various factors. Annual pruning can restore production and productivity in such trees. Chlorophyll, total sugars (TS), total phenolics (TP), and proline contents as well as polyphenol oxidase (PPO) activities, were measured in the 2005–2006 and 2006–2007 seasons in shoot buds with a few leaves in three mango cultivars (‘Amrapali’, ‘Mallika’, and ‘Dashehari’). Trees were grown at high density in an orchard and the aforesaid parameters were measured 1 month after different degrees of pruning (Stage I) and after subsequent fruit bud differentiation (FBD; Stage II). Severely-pruned mango trees had the highest contents of chlorophyll a, while chlorophyll b and total chlorophyll contents were found to be highest in moderately-pruned trees. Lightly-pruned trees had the highest contents of reducing sugars (RS), whereas TS contents were highest in severely-pruned trees. The contents of RS and TS increased in shoot buds during the FBD stage. A moderate intensity of pruning significantly increased TP contents, while the lowest TP contents were recorded in non-pruned trees. ‘Off’-year shoots had higher TP contents than ‘on’-year shoots. Irrespective of pruning intensity, shoot buds of ‘Mallika’ trees had the highest PPO activities, with lower levels in ‘Amrapali’ and ‘Dashehari’ shoot buds. PPO activities were reduced at the FBD stage in ‘on’-year shoots. Severely-pruned trees had the highest PPO activities, while the lowest PPO activities were recorded in lightly-pruned trees. Shoot bud proline contents were found to be highest in non-pruned trees, and decreased with increasing pruning intensity. Thus moderate pruning can be adopted in high density orchards to obtain sustainable production with improved maintenance of canopy architecture.     

Nutritional and cultural factors affecting rooting of papaya (Carica papaya L.) in vitro

Summary

Experiments were conducted to optimize nutritional and cultural requirements for initiation and growth of roots on papaya in vitro. Axillary shoots were obtained from plants which had been sub-cultured monthly for two years. Root initiation was enhanced when 1 to 2 mm of stem base was removed and shoots were growing actively before transfer to the rooting medium. Decreasing daylength during incubation from 24 h to 12 h promoted root initiation. Within the day temperature range of 22 to 29°C, optimum rooting occurred at 27°C and higher temperatures produced higher mean root weights per shoot. High concentrations of growth factors and the absence of sucrose in the medium both reduced root initiation, however, varying the concentration of sucrose and removing growth factors affected mean root weight per shoot. All media contained a modified de Fossard et al. (1974) basal medium plus 10 μM IBA.     

Effect of Planting and Harvesting Dates on Strawberry Fruit Quality under High Tunnels

ABSTRACT

There is an increasing demand in the market to improve strawberry quality by promoting human-health compounds content, as these may play a significant role in the prevention of chronic diseases. Strawberry cultivars, environmental conditions, and agronomical conditions have an effect on fruit characteristics; therefore, it is necessary to constantly generate information about the cultivar response to different production areas and cultural practices. The goal of this work was to evaluate the effect of two planting dates, two harvest dates, and four strawberry cultivars on total phenolic acid (gallic acid equivalent), ascorbic acid (vitamin C), and soluble solid content?titratable acidity-1 (SSC?TA-1) ratio in Huelva, Spain. Sixteen treatments resulted from the combination of four cultivars, two planting dates, and two harvest dates. Strawberry ‘Camarosa’, ‘Sabrosa’, ‘Aguedilla’, and ‘Fuentepina’ were selected for both seasons and planted on 7 Oct. (early planting) and 21 Oct. (late planting). Mid-February and mid-April were considered early and late harvest, respectively. Nutraceutical and organoleptic responses were specifics for each cultivar. The highest SSC?TA-1 ratio was observed in ‘Fuentepina’ planted late and harvested early. ‘Aguedilla’ resulted in the highest phenolic content when harvested in the late season. Additionally, phenolic content was significantly higher when using late planting combined with late harvest in most of the cultivars. Late harvested ‘Camarosa’ showed the highest TA concentration, whereas ‘Sabrosa’ resulted in the highest SSC regardless of harvesting date. Additionally, ‘Aguedilla’ and ‘Sabrosa’ showed the highest ascorbic content. Strawberry quality could be improved by selecting the adequate planting and harvesting dates according to specific cultivars.     

The Incorporation of Growth Hormones in Seed Dressings

Summary

The consequences of using ex vitro, single-node explants from different topophysical positions in chrysanthemum (Chrysanthemum grandiflorum /Ramat./ Kitam) were determined. In particular, how explant topophysis affected the rate of propagation, which is important for the successful micropropagation of chrysanthemum. Uniform shoots of five cultivars of chrysanthemum, cultured in vitro, were each divided into three equal zones: distal, central, and proximal. Two single-node explants were isolated from each zone and cultured on MS medium without any added growth regulators. After 10 weeks of culture, 50% of the shoots that had developed from axillary buds on each single-node explant were excised and measurements were taken in order to compare those shoots that had developed from explants from the different topophysical zones. The remaining shoots were sub-cultured on rooting medium. After 4 weeks, the numbers of roots per plantlet, and the total fresh weight (FW) of roots were recorded. The cultivars fell into two groups. ‘Lady Amber’, ‘Lady Orange’, and ‘Lady Vitroflora’ explants were topophysis-dependent, while ‘Lady Bronze’ and ‘Lady Rosy’ explants were topophysis-independent. For the three topophysis-dependent cultivars, the propagation rate, growth rate, shoot length, internode length, single leaf weight, and total plantlet FW values were highest for those shoots derived from the central and proximal zones. Topophysis failed to affect the number of leaves per shoot or the number of days between the appearance of two successive leaves. The effects of topophysis on the number of roots per plantlet and on root FW were inconsistent. The unequal growth of chrysanthemum plantlets during in vitro micropropagation can be an effect of topophysis, and this phenomenon is cultivar-specific in chrysanthemum.     

Induction of novel variants through physical and chemical mutagenesis in Barbeton daisy (Gerbera jamesonii Hook.)

Summary

Gerbera (Gerbera jamesonii) is an attractive ornamental flower of high economic importance. The present investigation was aimed at generating novel flower colour variants in the gerbera cultivar ‘Harley’ through physical and chemical mutagenesis. In vitro-raised shoot cultures of gerbera, established from petiole explants, were exposed to different doses of γ-rays (1.5, 2.0, 2.5, 5.0, 10.0, 15.0, 20.0, or 30.0 Gy) using a Cobalt-60 source emitting 2.51 kGy h^–1. To induce mutations through chemical mutagenesis, different concentrations of ethylmethane sulphonate [EMS; 0.1, 0.2, 0.5, 0.8, or 1.0% (v/v)] were administered for 10 min or for 20 min. The LD50 values calculated for shoot survival and the induction of mutations were approx. 6.5 Gy for γ-rays and 0.65% (v/v) EMS for 10 min, or ≤ 0.1% (v/v) EMS for 20 min. Investigations revealed a negative correlation between mutagen dose and plant survival, both in vitro and after acclimatisation. Morphological variants showing changes in leaf shape, leaf size, scape length, flower diameter, and flower colour were obtained. Significantly, early flowering was induced in all mutated plants compared to non-mutated plants.The high frequencies of colour variants obtained using Bγ-rays, or the application of EMS to in vitro-raised shoot cultures could be an effective way to improve gerbera cultivars.     

Biological control of the shoot disease of Amaranthus hybridus caused by Choanephora cucurbitarum with Bacillus subtilis

Summary

Isolates of Bacillus subtilis from soil and ogili (a local food condiment) controlled choanephora shoot disease of the vegetable crop plant, Amaranthus hybridus, in the greenhouse. Disease developed on plants inoculated simultaneously with the pathogen Choanephora cucurbitarum and the ‘ogili’ isolate, but not the soil isolate, of B. subtilis. Application of either bacterial strain to plants one day before a challenge with the pathogen prevented disease development. A single application of either strain prevented disease development from a subsequent challenge with the pathogen at any time over a thirty day period. Viable counts of the microflora on the shoot tips of the treated plants indicated strongly that the inoculated bacteria multiplied and colonized the extending shoot tip whether or not the shoots were covered with polythene bags. Both strains of Bacillus subtilis inhibited mycelial extension growth as well as conidial germination in vitro.     

Propagation of Black Currants from Single-Bud Cuttings

Black currants are readily propagated from single-bud hardwood cuttings approximately i inch long, with the bud at the top and planted vertically. The best part of the shoot from which to take such cuttings is the lower- mid portion (buds 15-22).

Optimum rooting is obtained from cuttings planted in January, February and March after dormancy has broken in the field, but by using 24-hour day-length successful rooting can be extended from October to March. The emergence of flowers in March-planted cuttings slightly reduces rooting.

Thirteen commercial varieties have been propagated successfully by this method.

Suitable softwood and semi- hardwood cuttings are available when the current season's shoots are 12 nodes or more in length, i.e. normally in late April. When these are planted in a propagation frame with soil heating, good rooting is obtained from April to June provided the subtending leaf is retained during the rooting period.

Twenty-four-hour day-length increases the rooting of cuttings planted in July; lack of rooting after July is attributed to early leaf abscission, the initiation of flowers and the onset of dormancy.