Synergism of citrus nematode (Tylenchulus semipenetrans Cobb.) and Colletotrichum gloeosporioides plays a major role in citrus dieback

Citrus is known as a major fruit due to its high nutritional value and adaptability in tropical and sub-tropical regions. Among diseases, citrus dieback is one of the most threatening diseases in which overall plant growth is reduced. Major causes are Colletotrichum gloeosporioides and citrus nematode (Tylenchulus semipenetrans) with 15-35% losses all over the world. Plant material was established adopting sanitary measures in earthen pots (12-inch diameter). Fresh culture of C. gloeosporioides and T. semipenetrans was prepared for the inoculation by following the standard procedures. In the first set, rootstocks were inoculated with 200mL of water having spore suspension of C. gloeosporioides while in in the second set, inoculation of T. semipenetrans was done by using 45 mL of water suspension having 2000 freshly hatched juveniles per pot, while at the rate of 1 × 107 spores/mL per plant. In the third set, the interaction of C. gloeosporioides and T. semipenetrans was studied by inoculating selected citrus rootstocks by both pathogens. After four months of inoculation, data were recorded on plant disease index (PDI) along with plant growth parameters (root weight, shoot weight, shoot weight, shoot length and number of leaves). Trifoliate orange and cox mandarin hybrid showed resistance against the development of T. semipenetrans while rough lemon, C-35 Citrange and sour orange were found susceptible. There was a significant difference in plant growth parameters between inoculated and healthy plants. Root weight and shoot weight decreased by 8.98g and 11.53g, while root length and shoot length decreased by 7.29cm and 13.5cm respectively as compared to control treatments in most susceptible rootstocks. Per cent Branch Infection (PBI) and per cent Disease Index (PDI) were maximum (71.52, 37) per cent on rough lemon respectively. Results regarding combined inoculation of C. gloeosporioides and T. semipenetrans showed that there was a significant difference in plant growth parameters between inoculated and healthy plants. In rough lemon, Root weight and shoot weight decreased by 13.86 and 20.57g respectively in diseased and healthy plants. Root length and shoot length decreased by 8.37 and 20.04cm respectively as compared to control treatments in most susceptible rootstocks. Overall results depicted that inoculation of both pathogens reduced plant growth more severely as compared to their individual application.

Pre-planting solutions for the slow decline of citrus caused by Tylenchulus semipenetrans.

The citrus nematode, Tylenchulus semipenetrans, is the causal agent of the slow decline of citrus. The nematode is well adapted to reproduce on citrus and very high densities are required to damage the trees and reduce yield. This chapter discusses the economic importance, geographical distribution, host range, damage symptoms, biology and life cycle, interactions with other pathogens, recommended integrated management, and management optimization of T. semipenetrans. Future research requirements and future developments are also mentioned.

Non-chemical based management of Tylenchulus semipenetrans, a major threat to the citrus industry

There is a vast variety of microbes available in soil performing diverse functions for plants including root colonization for protection against pathogens and nutrient acquisition. In the present study, efficacy of rhizospheric microbial strains and plant extracts were evaluated against citrus nematode for their nematicidal activity. Three different concentrations of plant extracts were evaluated in vitro, results depicts that 10% solution of Tagetes erecta (root) has given 46% the highest percentage mortality at 48hrs followed by Tagetes erecta (leaf) and Datura stramonium killed 41% and 37% nematodes respectively, similarly for 20% of plant extract in distilled water, the highest mortality rate was recorded for T. erecta (root) 68% followed by D. stramonium 47% and Acacia nilotica 44% at 48hrs of application. While using a higher concentration 30% of SS. the percentage mortality elevated multifold i.e. Marigold root has killed maximum 76% nematodes followed by Marigold leaves and Dhatura with mortality rate 69% and 58% respectively at 48 hrs of interval. While Eucalyptus killed lowest no of nematodes. Additionally, five bacterial isolates were evaluated for their nematicidal activity. Results indicated that for bacterial cell suspension, Pseudomonas putida has shown maximum mortality rate at 84% followed by Bacillus subtilis 73% & Pseudomonas geniculata 65% at 48hrs of interval. Similarly, in the 2nd set of experiment bacterial culture filtrates has exhibited promising results, maximum mortality rate was recorded for Bacillus spp. 81% followed by B. subtilis 76%, Ps putida 63%, after 48hrs of incubation. Moreover, an insight investigation of bacterial extracellular metabolites and plant extracts would enable researchers to develop purposeful products and compositions

IMPACT OF PLANT GROWTH PROMOTING RHIZOBACTERIA AS BIO-CONTROL AGENTS ON CITRUS NEMATODE, TYLENCHULUS SEMIPENETRANS INFECTING BALADY ORANGE (CITRUS SINENSIS L.) AND IMPROVING ITS PRODUCTIVITY

Three bacterial species of plant growth promoting rhizobacteria (PGPR) namely Paenibacillus polymyxa, Methylobacterium mesophilicum and Methylobacterium radiotolerans were tested alone or combined with humic acid as bio-control agents against the citrus nematode Tylenchulus semipenetrans under laboratory and field conditions. Results cleared that; all tested PGPR species produced IAA, HCN, ammonia, chitinase and protease enzymes and also solubilized phosphate in laboratory. P. polymyxa emphasized the superiority among other species in all PGPR properties except for phosphate solubilization, whereas M. radiotolerans showed highest amount of phosphorus solubilized in culture media. On the other hand, the results of the nematode survey conducted on orange, Citrus sinensis L. cv Balady grown in different localities of Ismailia and Sharkia Governorates during season 2019, revealed the presence of seven genera and species of plant-parasitic nematodes. Among which, T. semipenetrans occurred in all examined samples (100% frequency of occurrence) with a relatively high population density of 2330 and 2640 infected juveniles (J2) /250 g soil in Ismailia and Sharkia Governorates, respectively. Field experiments were conducted in two different locations, at Ismailia and Sharkia Governorates to assess the effectiveness of PGPR strains alone or combined to reduce the numbers of T. semipenetrans during season 2019. It was found that, all treatments caused significant (P≤0.05) reduction in T. semipenetrans population, compared to control treatment. The nematicide, Nemathorin® 10% G followed by P. polymyxa (20 L.fed-1 ) + foliarspraying of M. mesophilicm (5 L.fed-1 ) gave the highest efficacy in controlling the citrus nematode. Percentage reduction in numbers of J2/250g soil and adult females/1g roots for these treatments in Ismailia Governorate were 91% (85.7%) and 91.4% (89.5%), respectively. While the parallel values in Sharkia Governorate were 90% (87%) and 94% (90%), respectively. The combination of P. polymyxa and humic acid (20 L.fed-1 ) with foliar spraying of M. mesophilicm (5 L.fed-1 ) gained the third position. All treatments increased the fruit yield compared to control treatment. The highest percentages of increase were determined with Nemathorin (160% and 206%) followed by P. polymyxa + Humic acid (20 L.fed-1 ) + foliar spraying of M. mesophilicum (155.7% and 193%) and M. radiotolerans + P. polymyxa + foliar spraying of M. mesophilicum (153% and182%) in Ismailia, and Sharkia Governorates respectively.