Fusarium oxysporum f. sp. lycopersici retardation through induction of defensive response in tomato plants using a liquid formulation of Pseudomonas fluorescens (Pf1)

A liquid based Pseudomonas fluorescens (Pf1) bioformulation was found to contribute the restriction of Fusarium oxysporum f. sp. lycopersici in tomato roots by inducing defence enzymes. Induction of defence enzymes such as phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO), catalase, β-1,3 glucanase and super oxide dismutase (SOD), was studied in tomato plants pretreated with liquid as well as a talc based formulation of Pf1 challenged with F. oxysporum f. sp. lycopersici in glasshouse vegetable production systems. There were increased activities of PAL, PO, PPO, catalase and β-1 3-glucanases in tomato plants treated with a combined application of seedling dip?+?soil application?+?foliar spray of liquid and talc formulation of Pf1 when compared to pathogen inoculated and untreated healthy controls. The activities of the above enzymes started to increase at 3rd day, reached maximum levels on 8-9th day and thereafter declined gradually. Similarly, native polyacralamide gel electrophoresis (PAGE) analysis revealed that one to six isoforms of the defence enzymes each with a higher intensity were expressed in these treatments, whereas fewer isoforms with less intensity were noticed in inoculated controls. These results suggest that the retardation of the invasion of F. oxysporum f. sp. lycopersici in tomato roots resulting from treatment with the liquid formulation of Pf1 was due to enhancement of activities of enzymes involved in the phenylpropanoid pathway. These results suggest that induced systemic resistance occurred in the treated tomato plants.     

Evaluation of Induction of Systemic Resistance in Pepper Plants (Capsicum Annuum) to Phytophthora capsici Using Trichoderma harzianum and its Relation with Capsidiol Accumulation

The effect of pepper seed and root treatments with Trichoderma harzianum spores on necrosis caused in stems by Phytophthora capsici inoculation and on the course of capsidiol accumulation in the inoculated sites were studied. The results indicate that seed treatments significantly reduced stem necrosis, which fell by nearly a half compared with the values observed in plants grown from non-treated seeds. Necrosis was also reduced in plants whose roots were drenched with various doses of T. harzianum spores, although the extent of necrosis was not correlated with the dose used. Attempted isolation of P. capsici and T. harzianum from the zones immediately contiguous with the necrotic zones revealed the presence of the former but not of the latter, suggesting that there was no direct contact between them in the zones of isolation, which means that there was no competition for space. The percentage of P. capsici isolated 9 days after inoculation was greater in non-treated inoculated plants than in treated inoculated plants. These results suggest that T. harzianum, introduced into the subterranean part of the plant, induces a systemic defense response against P. capsici in the upper part of the plant. Analysis of capsidiol in the stems of treated inoculated plants by the end of the sixth day after inoculation, revealed that its concentration was more than seven-fold greater than in non-treated and inoculated plants, while after 9 days, the concentration of capsidiol decreased in the treated inoculated plants and increased in the non-treated inoculated plants. The high concentration of capsidiol detected in treated and inoculated stems after 6 days might be one of the contributing factors, but not necessarily the main factor, in delaying lesion development in the stems of pepper plants.     

Cellulysin induces downy mildew disease resistance in pearl millet driven through defense response

The responses to cellulysin as an immune inducer in pearl millet that confers downy mildew resistance mediated through lipoxygenase (LOX), a jasmonate-dependent enzyme involved in defence signalling, are discussed in this paper. The susceptible pearl millet cultivar 7042S was treated with cellulysin at 10, 15, 20, 30 and 50 μg/ml concentrations. All tested concentrations showed enhanced seed germination and seedling vigour when compared with the untreated control. Maximum seed germination of 92 % and seedling vigour was obtained following 20 μg/ml cellulysin treatment. Significant (P?<?0.05) downy mildew disease protection of 67 % and 71 % was observed when cellulysin was used at 20 μg/ml under greenhouse and field conditions, respectively. Further studies showed that the resistance induced by cellulysin treatment in pearl millet plant was systemic, required a minimum of 4 days to achieve maximum resistance development after pathogen inoculation seedling inoculation (five-day-old), and was sustained throughout the plant’s life. Plants raised from cellulysin-treated seeds and challenge inoculated at tillering (25-day-old) and inflorescence (45-day-old) showed persistence in resistance till the end of the crop period. A notable increase in LOX activity was observed in all the tested concentrations of cellulysin in plants inoculated with the pathogen at 24 h, compared to the control. However, a maximum 6-fold increase in LOX activity was noticed using a cellulysin concentration of 20 μg/ml 48 hours post inoculation. In contrast, glucanase (GLU) activity was high in control inoculated seedlings, but was low in cellulysin treated samples at all time intervals. The optimal cellulysin treatment (20 μg/ml) provided enhanced vegetative and reproductive parameters that resulted in higher yield compared to the untreated control.     

Preventive and curative activity of postharvest potassium silicate treatments to control green and blue molds on orange fruit

Preventive and curative antifungal activities of postharvest treatments with potassium silicate (PSi) against green (GM) and blue (BM) molds were evaluated on oranges (cvs. ‘Valencia’ or ‘Lanelate’) artificially inoculated in rind wounds with Penicillium digitatum and P. italicum, respectively. The most effective PSi concentration, the effect of fungal inoculum concentration, and the influence of temporal and spatial factors on antifungal activity were assessed in in vivo primary screenings. After 6 days of incubation at 20 °C, significant preventive (treatment before fungal inoculation) and curative (treatment after inoculation) activities against GM and BM were observed with PSi at 90 mM (GM and BM incidence reductions of 23 and 52 %, and 23 and 40 %, respectively). In preventive tests, the effectiveness of PSi was influenced by inoculum concentration (10³, 10⁴, 10⁵, or 10⁶ spores ml^-1), but not by the distance between treatment and inoculation sites (10, 20 or 30 mm). PSi applied about 2 h before inoculation showed higher preventive activity than applied before 24, 48 or 96 h. In order to determine the best dip treatment conditions, PSi at 90 mM was tested at 20 or 50 °C for 60 or 150 s in small-scale trials with ‘Lanelate’ oranges artificially inoculated before or after the treatment and incubated for 7 days at 20 °C. Dips at 20 °C for 60 s were selected and subsequently applied on inoculated ‘Valencia’ oranges stored at 5 °C and 90 % RH for up to 6 weeks. Curative postharvest dips effectively reduced the incidence and severity of both GM and BM during cold storage, while preventive dips significantly reduced the severity but not the incidence. Overall, postharvest PSi treatments showed potential as a new tool to be part of non-polluting strategies to control penicillium decay of citrus fruit.     

Avirulent strain of Colletotrichum induces a systemic resistance in strawberry

Strawberry plants exposed to an avirulent isolate of Colletotrichum fragariae acquired strong resistance against a virulent strain of C. acutatum. Biochemical, morphological and molecular markers indicated that the strong defence response was associated with an oxidative burst and a transient accumulation of salicylic acid (SA). A maximum accumulation of H₂O₂ and O₂ ^? was observed 8 h after inoculation (hai), callose was detected 48 hai, and a peak of SA was observed 48 hai. Biochemical and phytopathogenic analyses carried out in non-treated tissues revealed that the defence response was systemic and remained fully active 60 days after the first inoculation. Experiments also showed that the resistance acquired by mother plants after the inoculation with the avirulent isolate could be passed to daughter plants through runners. Further characterization of the induced systemic resistance showed that the resistance was not only effective against a virulent strain of C. acutatum but also against Botrytis cinerea.     

Effect of plant elicitors on the reproduction of the root-knot nematode Meloidogyne chitwoodi on susceptible hosts

Sustainable strategies for plant-parasitic nematode control are required to reduce dependence on chemical nematicides. Foliar application of various compounds can induce a systemic defence response that reduces nematode infestation. The effects of benzothiadiazole (BTH), β-aminobutyric acid (BABA), jasmonates (cis-jasmone and methyl jasmonate) and salicylic acid (SA) in the development and reproduction of the root-knot nematode Meloidogyne chitwoodi in tomato plants were assessed. The effects of BTH and of the jasmonates were further tested on potato plants. Pot assays were conducted using tomato plants cv. Tiny Tim or potato cv. Désirée treated with foliar sprays and inoculated with 300 second stage juveniles. Nematode development and reproduction were assessed 21 and 45 days after inoculation. Treatment with SA had a negative effect on nematode development in tomato plants but did not affect reproduction and methyl jasmonate treatment was the most effective in reducing nematode penetration (58 %). Nematode development was significantly affected in potato plants sprayed with cis-jasmone. Nematode penetration was reduced by 90, 67 and 81 % in plants treated with BTH, cis-jasmone and methyl jasmonate respectively, although the reproduction factor (Rf) was only significantly lower in the BTH treatment (Rf?=?7.6) when compared to the control (Rf?=?18.1). Our results suggest that both the SA and JA pathways play an important role in plant defence mechanisms against root-knot nematode development and reproduction for both plants, and should be considered in the design of integrated pest management approaches.     

Comparison of root and foliar applications of potassium silicate in potentiating post‐infection defences of melon against powdery mildew

The application of silicon to the roots or leaves reduces the severity of powdery mildew (Podosphaera xanthii) in melon but the latter treatment is less effective. This study compared key biochemical defence responses of melon triggered by P. xanthii after root or foliar treatment with potassium silicate (PS). Treatments consisted of pathogen‐inoculated or mock‐inoculated plants supplied with PS via roots or foliarly, as well as a non‐treated control. The activity of defence enzymes and the concentration of phenolic compounds, lignin and malondialdehyde were determined from leaf samples at different time points after inoculation. Pathogen‐inoculated plants irrigated with PS showed both an accumulation of silicon and primed defence responses in leaves that were not observed in pathogen‐inoculated plants either sprayed with PS or not treated. These responses included the anticipated activity of peroxidase and accumulation of soluble phenols, the activation of chitinase and repression of catalase, and the stronger activation of superoxide dismutase, peroxidase and β‐1,3‐glucanase. Moreover, the lignin concentration increased in response to inoculation, whereas the malondialdehyde concentration decreased. For the foliar treatment, however, only an increase in lignin deposition was observed compared with the control plants. The results show that silicon strongly plays an active role in modulating the defence responses of melon against P. xanthii when supplied to the roots as opposed to the foliage.     

Induction of defence related enzymes and phenolic compounds in lupin (Lupinus albus L.) and their effects on host resistance against Fusarium wilt

Two different biotic inducers [Pseudomonas fluorescens and Pseudomonas putida] and three different abiotic inducers [copper sulphate, indole butyric acid and potassium chloride] were tested for their efficacy in inducing resistance in lupin plants against Fusarium wilt disease caused by Fusarium oxysporum f. sp. lupini. Application of the biotic and abiotic inducers as seed treatments significantly reduced wilt disease incidence under greenhouse and field conditions. Potassium chloride and Pseudomonas fluorescens were superior. A time course of defence-related enzymes showed substantial increases in enzyme activities in induced infected seedlings compared with untreated healthy plants or infected controls. However, the magnitude of the increase varied among treatments. The maximum increases in chitinase and ??- glucanase activities were recorded at 12 and 8?days after inoculation with the pathogen, respectively. Also, the activity of phenylalanine ammonia lyase increased dramatically 8?days after inoculation. Greater accumulation of phenolic compounds and specific flavonoids upon infection with the pathogen was found in induced and/ or infected seedlings compared with healthy plants. In addition to inducing disease resistance, the treatments were accompanied by significant increases in crop parameters and seed yield compared with untreated controls.     

Biochemical responses associated with common bean defence against Sclerotinia sclerotiorum

The aim of this study was to investigate changes in defence compounds of common bean cultivars with different levels of resistance to the fungus Sclerotinia sclerotiorum and determine the relation of the compounds to pathogen tolerance. The lines were inoculated with the pathogen and assessed for enzymatic and non-enzymatic parameters related to plant defence: peroxidases (POX), polyphenol oxidases (PPO), catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX), total soluble phenol and lignin contents. Stem tissue samples were collected from two regions of the plant for biochemical analyses. Stem tissue samples were collected from two regions of the plant for biochemical analyses. In the position one, 5 cm of the stem was collected from the region with necrosis caused by the pathogen, and in the position two, 5 cm of the stem was collected from the end of the position one at the times of 12, 24, 48, 72, 96 and 120 h after inoculation (HAI). Greater lignin and total soluble phenol contents and greater induction of POX and SOD activity in inoculated plants in the region near the inoculation (position one) indicate local activation with later signalling for activation of defence mechanisms in other regions of the plant. The genotype with a greater level of resistance was superior to the susceptible one in regard to lignin production and the activities of POX, APX and SOD defence enzymes. These results suggest that a combination of these defence responses in common bean may contribute to greater plant resistance to the pathogen and that these enzymes have potential use in selection of common bean genotypes.     

The Effects of Organomercury Seed Treatment on Barley Artificially Inoculated with Fusarium spp.1

Artificial field inoculation showed that in one year out of two, Fusarium roseum caused significant yield loss in barley grown from organomercury-treated seed. No significant yield loss occurred in either year as a result of inoculation with Fusarium nivale. Results from field, pot and blotter tests suggested that inoculation with F. nivale and sometimes F. roseum could at times be associated with increased vigour in barley. There was a fairly consistent trend particularly with F. nivale for this to occur to a greater extent in plants from untreated seed than in those from treated seed. Similarly, any reductions in vigour associated with inoculation with more pathogenic strains of either species occurred only, or to a greater extent, in plants from treated seed. There was some evidence of an increased capacity for regenerative root and shoot growth in barley plants damaged by Fusarium inoculation, and it is suggested that increased growth may be associated with increases in percentage dry weights of the shoot 8 but not 18 days after inoculation. In the absence of inoculation, the effect of seed treatment was to increase grain yields, though this was not clearly associated with the increases it sometimes caused in emergence and in 1000-grain weight.     

Induction of resistance to Sclerotium rolfsii in different varieties of onion by inoculation with Trichoderma asperellum

We evaluated the ability of Trichoderma asperellum Samuels, Lieckfeldt & Nirenberg to induce resistance to the fungal plant pathogen, Sclerotium rolfsii Saccardo, in three onion (Allium cepa L.) varieties. Both the severity of disease and the activities of glucanase, chitinase and peroxidase (enzymes involved in plant resistance) were evaluated in onions inoculated with T. asperellum alone, S. rolfsii alone, or both T. asperellum and S. rolfsii (dual-inoculation) and compared to uninoculated (control) plants. In dual inoculations, the presence of T. asperellum reduced the severity of disease symptoms caused by S. rolfsii. Inoculation with T. asperellum alone increased glucanase, chitinase and peroxidase activity in bulbs, roots and leaves of all three onion varieties compared to uninoculated controls; bulbs of the variety Red Satan (RS) had the highest enzyme activity. In plants inoculated with S. rolfsii alone, enzyme activity was only increased in bulbs and roots compared to uninoculated controls. The highest levels of enzyme activity also occurred only in bulbs and roots of plants that had been dual-inoculated with T. asperellum and S. rolfsii. Plants of the RS variety showed the highest enzyme activities (both constitutive and induced) and showed the lowest severity of disease. Therefore, application of T. asperellum has potential as a biological control alternative to synthetic fungicides for protection of onion crops against infection by S. rolfsii. This protection depends on both constitutive and induced defence responses and varies amongst onion varieties.     

Activation of tomato plant defence responses against bacterial wilt caused by Ralstonia solanacearum using DL-3-aminobutyric acid (BABA)

In this study, we investigated the ability of DL-3-aminobutyric acid (BABA) to protect tomato against bacterial wilt caused by Ralstonia solanacearum. This was combined with studies of accumulation of total phenolic compounds, free and total salicylic acid (SA), and activity of enzymes related to plant defence, i.e., polyphenol oxidase (PPO) and catalase (CAT). Under greenhouse conditions, tomato plants pre-treated by soil drenching with BABA profoundly reduced disease severity of bacterial wilt compared to plants receiving a soil drench with water. Thus, BABA reduced leaf wilting index by 75.3 % and vascular browning index by 69.9 %, without any in vitro inhibitory activity on the pathogen. BABA treatment significantly reduced the population of R. solanacearum in stems of tomato plants and additionally also significantly increased both fresh and dry weight of roots and shoots of tomato plants compared with the inoculated control. Application of BABA resulted in a high increase in PPO activity both in plants with and without inoculation. Compared to water-treated plants, treatment with BABA also induced a significant increase of total phenolic compounds as well as of free and total SA in leaves of both inoculated and non-inoculated tomato plants at all sampling times. CAT activity decreased in tomato plants treated with BABA in comparison with the water-treated control plants and the decrease in activity correlated with an increasing total SA accumulation. These findings suggest that BABA treatment resulted in induction of resistance to bacterial wilt in tomato.     

Biological control mechanisms of D-pinitol against powdery mildew in cucumber

D-pinitol is an effective agent for controlling powdery mildew (Podosphaera xanthii) in cucumber. In this study, we determined the mechanisms of D-pinitol in controlling powdery mildew in cucumber plants. We compared P. xanthii development on cucumber leaf surface treated with D-pinitol or water (2 mg ml⁻¹) at different time points after inoculation. The germinating conidia, hyphae, and conidiophores of the pathogen were severely damaged by D-pinitol at any time of application tested. The highest level of suppression of fungal development was obtained at 3 days after inoculation. The contents of chlorophyll, total phenolics, flavonoid, and gallic acid and its derivatives (GAD); the activities of phenylalanine ammonialyase (PAL), polyphenoloxidase (PPO), peroxidase (POX), and superoxide dismutase (SOD); and the expression of the genes encoding for PR-1, peroxidase (POX), lipoxygenase (LOX1), chitinase (Chit1) were higher in the cucumber leaves treated with D-pinitol and inoculated than in the leaves either treated with D-pinitol or inoculated with the pathogen. These results suggest that D-pinitol triggers several plant defense responses in cucumber leading to pathogen suppression and resistance to powdery mildew.     

Inoculation with <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis>, cause of stem rot in Jerusalem artichoke,under field conditions

Stem rot caused by Sclerotium rolfsii is an important problem of Jerusalem artichoke, and breeding of Jerusalem artichoke for resistance to stem rot requires effective screening methods. The objective of this study was to compare methods for inoculating Jerusalem artichoke with S. rolfsii under field conditions. A 4 × 2 × 3 factorial in a randomized complete block with four replications was used in two environments characterized by different rates of fertilizer application (recommended rate and low rate) in the rainy season. The factors included four Jerusalem artichoke varieties (HEL280, HEL278, HEL256 and JA49), two levels of wounding (wounded and not wounded) and three methods of inoculation. The inoculation methods consisted of: 1) non-inoculated natural infection; 2) attaching one colonized sorghum seed at the crown of plants (single sorghum seed method); and 3) spreading 30 g m^?2 of colonized sorghum seeds (broadcast inoculation method). Jerusalem artichoke varieties and inoculation methods were significantly different for disease incidence, whereas the difference between wounded and non wounded treatments was not significant. Significant interactions were found between the variety and wounding method, the variety and inoculation method, wounding method and inoculation method, and inoculation method and environments. Natural infection resulted in the lowest disease incidence (32.2 %), whereas the single sorghum seed and the broadcast inoculation methods had a high disease incidence (79.0 % and 77.3 % respectively) and were not signnificantly different from each other. Broadcast inoculation did not allow differentiation of Jerusalem artichoke varieties for disease incidence, whereas single seed inoculation could better identify the differences among Jerusalem artichoke varieties.     

Control of light leaf spot and clubroot in brassica crops using defence elicitors

Plant defence elicitors are compounds that can induce host defence responses against plant pathogens and offer a novel strategy for disease management. Disease control by elicitors can be inconsistent and is often dependent on the crop, the variety and the environment. The use of foliar application of defence elicitors to control light leaf spot (LLS) disease caused by Pyrenopeziza brassicae in the brassica crops winter oilseed rape (WOSR) and Brussel sprouts was evaluated in field trials across multiple years. Elicitor responses in WOSR varied between years. Yield benefits were also inconsistent and did not reflect the level of disease control. Results with Brussel sprouts were more consistent although variation between variety, trial site and year were observed. In particular the salicylic acid analog Acibenzolar-S-Methyl, in the commercial product Bion®, demonstrated good disease control across the field trial sites in the early maturing Brussel sprout variety Cobus. Levels of LLS were consistently reduced when Bion® was alternated within a standard fungicide programme, applied as an individual spray or in combination with other defence elicitors. When applied as a root drench or seed soak Bion® also reduced symptom development of the soil-borne brassica disease clubroot, caused by Plasmodiophora brassicae, in WOSR. These results indicate that defence elicitors such as Bion® can be used as an additional disease management tool alongside host resistance and standard fungicide programmes to protect brassica crops.     

Studies into primary and secondary infection processes by Plasmodiophora brassicae on canola

The early stages of infection of canola roots by the clubroot pathogen Plasmodiophora brassicae were investigated. Inoculation with 1 × 10⁵ resting spores mL^?1 resulted in primary (root hair) infection at 12 h after inoculation (hai). Secondary (cortical) infection began to be observed at 72 hai. When inoculated onto plants at a concentration of 1 × 10⁴ mL^?1, secondary zoospores produced primary infections similar to those obtained with resting spores at a concentration of 1 × 10⁵ mL^?1. Secondary zoospores caused secondary infections earlier than resting spores. When the plants were inoculated with 1 × 10⁷ resting spores mL^?1, 2 days after being challenged with 1 × 10⁴ or 1 × 10⁵ resting spores mL^?1, secondary infections were observed on the very next day, which was earlier than the secondary infections resulting from inoculation with 1 × 10⁷ resting spores mL^?1 alone and more severe than those produced by inoculation with 1 × 10⁴ or 1 × 10⁵ resting spores mL^?1 alone. Compared with the single inoculations, secondary infections on plants that had received both inoculations remained at higher levels throughout a 7‐day time course. These data indicate that primary zoospores can directly cause secondary infection when the host is under primary infection, helping to understand the relationship and relative importance of the two infection stages of P. brassicae.     

Phenmedipham–Ozone Pollution Interactions in Sugarbeet (Beta vulgaris L. cv. Saxon): A Physiological Study

Actively growing sugarbeet is treated with the post-emergent herbicide phenmedipham at times when ozone pollution episodes are likely to occur. There is a possibility of an interaction occurring between ozone and phenmedipham as both treatments produce similar effects in susceptible plants, such as a reduction in growth and photosynthesis and an increase in the activities of endogenous antioxidant enzymes. To investigate this likelihood, laboratory experiments were conducted in which two- to three-leaf sugarbeet plants (Beta vulgaris L. cv. Saxon) were exposed to a simulated two-day ozone episode (100 nl litre⁻¹, 7 h day⁻¹) followed three days later by treatment with field rate phenmedipham (1·14 kg AI ha⁻¹). Growth analysis indicated that an interaction was occurring in which plants treated with ozone and phenmedipham had less reduction in shoot fresh weight than expected. Exposure to phenmedipham alone or ozone followed by phenmedipham reduced net photosynthesis by over 50% and transpiration rate by 30%. The activities of antioxidant enzymes such as catalase, guaiacol peroxidase and superoxide dismutase were stimulated by both treatments individually, but to a greater extent when ozone and phenmedipham were combined. For example, three days after herbicide treatment, the activity of superoxide dismutase increased by 20% in plants treated with ozone alone, 20% in plants treated with phenmedipham alone and 85% in plants that were treated with ozone followed by phenmedipham. We conclude that ozone pollution may predispose sugarbeet to tolerate the herbicide phenmedipham by enhancing the activity of the endogenous antioxidant detoxification enzyme system.     

Induction of systemic disease resistance and pathogen defence responses in Asparagus officinalis inoculated with nonpathogenic strains of Fusarium oxysporum

The ability of nonpathogenic isolates of Fusarium oxysporum (np Fo ) to induce systemic resistance and defence responses against subsequent challenge with a pathogenic strain of F. oxysporum f. sp. asparagi ( Foa ) was examined in Asparagus officinalis . In a split-root experiment, roots inoculated with np Fo exhibited a hypersensitive response and those subsequently inoculated with Foa displayed resistance. Induction of systemic resistance in np Fo -treated plants led to significantly fewer necrotic lesions ( P  = 0·05) and reduced Foa disease severity compared with plants not treated with np Fo . In hyphal-sandwich root inoculation experiments, activities of peroxidase and phenylalanine ammonia-lyase and lignin content were higher in np Fo -treated plants and increased more rapidly than in np Fo -untreated plants after Foa inoculation. Antifungal activity (inhibition of fungal spore germination and germ-tube growth) from exudates of roots inoculated with Foa were observed for np Fo -treated plants but not for np Fo -untreated plants. Thus, isolates of np Fo may function as inducers of systemic acquired resistance (SAR) and defence responses against Foa invasion in A. officinalis .     

Differential response to combined prochloraz and thyme oil drench treatment in avocados against the control of anthracnose and stem-end rot

The ability to meet consumers demand for high-quality standard fruit entails the distribution of unblemished safe fruit free of chemical residues on its edible portion. Therefore, this study was focused on investigating the influence of the combined effect of aqueous plant volatiles with half strength prochloraz solution to control anthracnose and stem-end rot in the green-skinned avocado cultivar (Fuerte). This method was applied due to its practicability on bulk fruits in packhouses and the fruits were subjected to stand-alone and combined treatments to assess the development of the disease after cold storage and observe the elicitation of the residual effect of the treatments on the defence related enzymes in ‘Fuerte’. The incidence of stem-end rot was 10% by the combination of prochloraz® (500 μg mL^?1; P50) with 0.1% v/v thyme oil compared to the 58.8% incidence exhibited by the untreated fruit during storage at 6.5 °C for 14 days followed by 3 days at retail shelf conditions (15 °C) (preventative application). Citral (0.1% v/v), P50 (500 μg mL^?1)?+?0.1% v/v citral and yucca extract alone reduced the stem-end rot incidence to about 25% during storage. More so, thyme oil (0.1% v/v) reduced both anthracnose and stem-end rot incidence to 35% after postharvest storage and P50 (500 μg mL^?1)?+?0.1% v/v thyme oil and 0.1% v/v thyme oil effectively induced the activity of phenylalanine ammonia lyase, chitinase and β-1, 3 glucanase in fruit inoculated with Lasiodiplodia theobromae and Colletotrichum gloeosporioides through the improvement of quality and firmness of the fruit after storage.