الفهرس 
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Abstract
Economical losses for freshly harvested fruits and vegetables were caused greatly by postharvest pathogens. Each of fungi and bacteria are responsible for postharvest diseases. Fungal biocontrol products with pesticidal activity are being explored in order to make available as biopesticides, which are easily biodegradable, selective and can be easily produced, especially after the wide range of harm effects of synthetic pesticides. In many cases fungi are considered equally responsible for rapid spoilage. Numerous minutes’ spores or conidia are produced by fungi, and these structures distribute readily in the surrounding causing rapid spoilage of vegetables and fruits.
In this study, postharvest rots of sugarbeet were caused by fungi. The isolated fungi were Aspergillus, Fusarium, and Rhizopus. These pathogens were previously reported and described as serious postharvest pathogens causing rapid spoilage of vegetables and fruits. Biological control is one of most promising alternatives method to fungicides, whereas, microorganisms of biocontrol agents protect fruits and vegetables from phytopathogens infection. Trichoderma as a biological control agent has been proved to suppress certain diseases in a great number of studies In this investigation the potentials of T. harzianum (T3 and T24) as antagonists in suppressing fungal postharvest sugarbeet roots pathogens were examined, whereas, some of these fungal pathogens were previously reported as heavy losses in storage and transit of beet. Moreover, these types of studies will addresse the antagonistic actions of T. harzianum against some isolated fungal postharvest pathogens of sugarbeet. The tested T. harzianum had inhibitory effect against these fungal pathogens which could be suggested to produce extracellular metabolites that have potential to control sugarbeet fungal root rot.
The results obtained can be summarized as follows:
A total of six fungal pathogens were isolated from healthy or rotten sugarbeet roots. All of these isolates were identified morphologically on the basis of colony, hyphal morphology of fungi cultures and spores characteristics. The six isolated postharvest fungal pathogens of sugarbeet were belonged to three genera and five different species. These fungal pathogens were identified as Rhizopus sp., A. flavus and Fusarium sp. (1) from the diseased sugarbeet, whereas, Rhizopus sp., A. niger and Fusarium sp. (2) from healthy roots.
The percentage frequency of the isolated fungi from healthy (Groups I) and diseased (Groups II) of sugar the tested samples of beet roots were calculated. Mycological analysis of rotten sugarbeet samples (Grousp II) showed three fungal species belonged as three genera. Rhizopus sp. caused rotting in 60% of the examined diseased sugarbeet roots. A. flavus and Fusarium sp. (1) came next with 20% for each of the total samples. According to healthy beets of group (I), Rhizopus sp. was recorded again as high frequency of occurrence (50%) followed by A. niger (40%). Finally, healthy beet roots in group (I) reported the low frequency of occurrence for Fusarium sp. (2) which represented 10% of samples.
In Pathogenicity test, the concentration of pathogen spore suspension had significant effect on the effectiveness of pathogenicity, whereas, CFU of the higher concentration (107 CFU ml-1) gave the greater decay indices for most pathogens (for example, DI, 270, Rhizopus sp.) at the incubation period of 7-days. Moreover, prolongation of incubation period of roots with pathogen, the greater Decay Index was recorded.
In this study the all tested fungi were virulent; however, Rhizopus sp. was the most virulent pathogen showing the highest decay index for all examined concentrations (105, 106, 107 CFU ml-1). A. flavus showed a little number of lesions (-ve effect) after the three tested incubation periods using either low or high concentration of spore suspension
Colony growth diameter and daily growth rate of Rhizopus sp. on the three tested solid media (sugarbeet juice agar, Czapek’s agar and PDA) was faster and it reached to the end of Petri dish (9 cm) in two days of incubation. Growth of the all tested fungal organisms was promoted in various degrees on PDA or sugarbeet juice agar media when compared with their growth on Czapek’s agar medium; except for the antagonists (T3 and T24) in which the mycelial growth was lowered on beet extracts comparing with Czapek’s agar medium.
Behavior of fungal growth on liquid media for all the tested postharvest sugarbeet fungal pathogens showed the same pattern of growth in liquid media of PDB, Cz and beet extract, whereas, the measured dry weights increased in beet extract comparing with the other two liquid media after 7 days of incubation period.
In vitro antagonistic tests of Trichoderma isolates by dual agar plates, first contact between the antagonists and any of the four tested fungal pathogens was observed within three days of incubation, except for Rhizopus sp., where contact came earlier (two days). There are different degrees of antagonism by T. harzianum (T3 and T24) against the tested postharvest fungal pathogens. In dual plates, clear zone was observed after the 3rd day of incubation, in addition size of clear zone varied between treatments according to the phytopathogen and the antagonist
There was no correlation between zone of inhibition and the occurrence of overgrowth by antagonists. T3 showed wide clear zone against A. niger and Fusarium spp. and couldn’t able to overgrow it.
The gaseous organic volatile metabolites released by the antagonists inhibited the growth of the tested postharvest pathogens that inoculated in the inverted Petri dish agar plates, whereas, the microbial growth of pathogen was remarkably restricted. The maximum inhibition was 55.84 % and produced by T. harzianum T3 against A. niger after 5 days of incubation period. The weakest recorded effect of VOCs by the tested antagonists was shown against Rhizopus sp. Postharvest pathogens were greatly inhibited by VOCs produced by T. harzianum T3 and T24 as well as mint oil.
The test of non-volatile organic compounds (non-VOCs) production by the two tested Trichoderma spp. (T3 and T24) against postharvest fungal pathogens of sugarbeet was evaluated, whereas, clear zones were formed in well diffusion test on agar plates and zones of inhibition reached to 0.69 cm. The low sensitive phytopathogen is Fusarium spp. of the all tested pathogens, which showed no clear zone of inhibition by Trichoderma non-VOCs.
The effects of T. harzianum (T3 and T24) culture filtrates (different concentrations) as well as mint oil on spore germination of postharvest fungal pathogens were evaluated. In the case of Fusarium sp. (1) infection, all treatments were the higher as positive effect either by mint oil or culture filtrates of T. harzianum (T3 and T24), especially samples of sugarbeet roots where seeds planted with mint oil, in which calculation of Decay Index (DI) gave zero infection (100% protection) by all treatments. Fusarium sp. (2) came to next of positive effect of the treatments and in some investigation the protection reached to 100% with zero infection.
On the other hand, results of treatments with mint oil or 100% culture filtrate concentration of T3 and T24 represented high efficiency of sugarbeet protection from rotting by the postharvest pathogens Rhizopus sp. and A. niger in which the protection for some cases became nearly 100% for 3 and 5 days of incubation period compared with the other culture filtrate concentrations (25 and 50%) in which protections were lower. The high degree of DI was represented by Rhizopus sp. which was the most aggressive pathogen for untreated (+ve) samples (seed planted without mint oil), and the infected only presented 356 DI after 7 days incubation period. However, the same infected samples represented 32.8 DI when it was treated with 100% culture filtrate concentration of T24 after the same incubation period
Samples of sugarbeet roots in which seeds were treated with mint oil before planting showed high response of protection after treatment with mint oil or culture filtrates of T3 and T24 compared with sugarbeet roots samples of seeds untreated with mint oil.
Slice assay results clearly indicate that sugarbeet slices had a complete protection from the infection by root pathogens when treated with T. harzianum (T3 and T24). Moreover, mint oil protected suagrbeet slices from rotting pathogens in which the efficacy of mint oil action equal T. harzianum T3 and T24 spore suspension antagonistic action on suppression of postharvest fungal pathogens.
The untreated control slices that inoculated with pathogen only showed a remarkable rot, while rot decreased in treated slices with either mint oil or spore suspension of T. harzianum isolates (T3 and T24). Generally, mint oil efficacy for suppression of postharvest pathogens on beet slices was mostly superior to those of Trichoderma spore suspension.
In the test of beet storage temperatures effects on sugarbeet root rot, the loss index has been taken into consideration in all examined storage temperature. Storage temperatures of 30 and 40oC represented severe (++++) loss index (76-100%) after storage in two weeks, and it seems to have fast rot with storage time, hence losses are starting earlier. In addition, beet roots wouldn’t stay healthy at least one week.
Samples of storage at 0 and 2-5oC have the lowest beet loss index, whereas, no sugarbeet rot (-, loss index) till 6 weeks for storage temperature at 0oC, however, low rot (+) stared for samples of 2-5oC after 3 weeks, in which severe rot (++++) became clear shown after 6 weeks of storage. In addition, beet roots would stay healthy for around two weeks under these conditions. On the other hand, samples stored at 10 or 20°C both showed the same pattern exactly, where sever rot (++++) reached for sugarbeet roots after 4-5 weeks of storage
As previously mention in results that the best temperature for storage of beet roots were 2-5, 10 and 20oC. These temperatures were chosen to be tested again in storage of sugarbeets that treated with culture filtrates of the antagonists combined with the chosen essential oil (mint oil).
Our results show that the incidence of natural decay in sugarbeet root after postharvest spraying with Trichoderma culture filtrate (T3) mixed with mint oil was lowered than that in the untreated samples after storage at 2-5, 10 and 20oC, and it took 3 weeks to start low rot (loss index, +) for treatments of 50% concentration of culture filtrate, however, low rot started for beets at 4 weeks of treatments with 100% concentration.
Severe rot of loss index (++++) for sugarbeet roots treated with 100% concentration of Trichoderma (T3) culture filtrate used 10 weeks for the tested lower temperatures of storage (2-5 and 10oC), however, the same extent of loss index at 20oC came one week earlier (9 weeks). Generally, the treated beet roots would stay healthy for long period (3-4 weeks) comparing with untreated at the same conditions. Furthermore, our findings indicate that the inhibitory effect of postharvest spraying with Trichoderma culture filtrate and mint oil on natural decay in beet root is directly proportional with the concentration of application (50% or 100%).
Comparing with the untreated beet root the treated samples at the same tested temperatures, severe rot (++++) of loss index came earlier to be after 9-10 weeks of storage period by using mint oil and culture filtrates of the antagonists. This means that, more sugarbeets now have to be healthy and stored for a longer period till reach severe rot.
The significance of developing biodegradable and eco-friendly products to be as natural fungicides in the management and controlling various postharvest plant pathogens become the subject of increasing interest. Trichoderma harzianum (T3 and T24) has a potential of being used to develop a biopesticide which would be useful in the control of postharvest root rot pathogens of sugarbeet roots.