Guava Decline Research Articles

Densidade inicial de inóculo, época de avaliação e reprodução de Meloidogyne enterolobii em goiabeira 'Paluma'

ABSTRACT Guava decline is a complex disease caused by the interaction between Meloidogyne enterolobii and Neocosmospora falciformis (Syn.: Fusarium solani). Thus, selecting M. enterolobii-resistant genotypes within the genus Psidium is essential for controlling this disease, and developing a resistant cultivar of Psidium guajava could significantly impact this issue. Thus, the objective of this study was to assess the response of the guava plants of the cultivar Paluma to different densities of M. enterolobii inoculum. Guava seedlings were inoculated with 500, 1,000, 5,000, 10,000, and 20,000 eggs + second-stage juveniles (J2) of M. enterolobii per plant. Root and shoot fresh weights, shoot dry weight, root length, plant height, and stem base diameter were evaluated at 70 and 135 days after inoculation (DAI). Total number of M. enterolobii eggs + J2 in the root system and nematode reproduction factor nematode were assessed. Nematode multiplication in roots was not proportional to increases in initial inoculum density; thus, the best plant responses to nematode multiplication in the evaluated cultivar were found for the lowest tested densities. The reproduction factor decreased as the inoculum density was increased, at both evaluations (70 and 135 DAI).

Preservação de genótipos moderadamente resistentes ou tolerantes: uma estratégia para suplantar o declínio da goiabeira

ABSTRACT: Native to the tropical Americas, guava (Psidium guajava L.) is an important crop in Brazil. However, the emergence of so-called guava decline, a complex disease resulting from root parasitism by the root-knot nematode (Meloidogyne enterolobii Yang & Eisenback) in association with opportunistic fungi, has decimated guava orchards across Brazil and in other countries. In the present study, seminiferous guava accessions were vegetatively propagated by minigrafting and their genotypes preserved for resistance reassessment in clones to confirm or not host plant reactions. The results indicated a highly virulent parasite, high host suitability of the P. guajava species, and widely varying reactions among plants of the same genotype and between different genotypes, demonstrating that the strategy of preserving the germplasm and reassessing reactions in clones may be important in identifying and selecting germplasms with a degree of resistance to M. enterolobii. The progeny of cv. Paluma P02R5R2 obtained the lowest average parasite reproduction factor (RF = 22.11) among the genotypes evaluated and was; therefore; classified as moderately resistant and preserved for future research.

Meloidogyne enterolobii-induced Changes in Guava Root Exudates Are Associated With Root Rotting Caused by Neocosmospora falciformis.

Despite the worldwide importance of disease complexes involving root-feeding nematodes and soilborne fungi, there have been few in-depth studies on how these organisms interact at the molecular level. Previous studies of guava decline have shown that root exudates from Meloidogyne enterolobii-parasitized guava plants (NP plants), but not from nematode-free plants (NF plants), enable the fungus Neocosmospora falciformis to rot guava roots, leading to plant death. To further characterize this interaction, NP and NF root exudates were lyophilized; extracted with distinct solvents; quantified regarding amino acids, soluble carbohydrates, sucrose, phenols, and alkaloids; and submitted to a bioassay to determine their ability to enable N. falciformis to rot the guava seedlings' roots. NP root exudates were richer than NF root exudates in amino acids, carbohydrates, and sucrose. Only the fractions NP-03 and NP-04 enabled fungal root rotting. NP-03 was then sequentially fractionated through chromatographic silica columns. At each step, the main fractions were reassessed in bioassay. The final fraction that enabled fungal root rotting was submitted to analysis using high performance liquid chromatography, nuclear magnetic resonance, mass spectrometry, energy-dispersive X-ray fluorescence, and computational calculations, leading to the identification of 1,5-dinitrobiuret as the predominant substance. In conclusion, parasitism by M. enterolobii causes an enrichment of guava root exudates that likely favors microorganisms capable of producing 1,5-dinitrobiuret in the rhizosphere. The accumulation of biuret, a known phytotoxic substance, possibly hampers root physiology and the innate immunity of guava to N. falciformis.

Evaluation of bio-control agents for the management of guava decline

Evaluation of bio-control agents for the management of guava decline

Diversity, phylogeny and evolution of the rapidly evolving genus Psidium L. (Myrtaceae, Myrteae).

Psidium is the fourthth largest genus of Myrtaceae in the Neotropics. Psidium guajava is widely cultivated in the tropics for its edible fruit. It is commercially under threat due to the disease guava decline. Psidium cattleyanum is one of the 100 most invasive organisms in the world. Knowledge of the phylogenetic relationships within Psidium is poor. We aim to provide a review of the biology, morphology and ecology of Psidium, a phylogenetic tree, an infrageneric classification and a list of species. Morphological and geographic data were obtained by studying Psidium in herbaria and in the field between 1988 and 2020. Forty-six herbaria were visited personally. A database of approx. 6000 specimens was constructed, and the literature was reviewed. Thirty species (about a third of the species in the genus) were sampled for molecular phylogenetic inference. Two chloroplast (psbA-trnH and ndhF) and two nuclear (external transcribed spacer and internal transcribed spacer) regions were targeted. Phylogenetic trees were constructed using maximum likelihood (ML; RaxML) and Bayesian inference (BI; MrBayes). Psidium is a monophyletic genus with four major clades recognized as sections. Section Psidium (ten species), to which P. guajava belongs, is sister to the rest of the genus; it is widespread across the Neotropics. Section Obversifolia (six species; restricted to the Brazilian Atlantic Forest), which includes P. cattleyanum, is sister to the innermost clade composed of sister sections Apertiflora (31 species; widespread but most diverse in the Brazilian Atlantic Forest) + Mitranthes (26 species; widespread in dry forests and probably diverse in the Caribbean). Characters associated with diversification within Psidium are discussed. Research on pre-foliation, colleters, leaf anatomy, leaf physiology, staminal development, placentation and germination associated with the anatomy of the opercular plug is desirable. Studies are biased towards sections Psidium and Obversifolia, with other sections poorly known.

Greenhouse and field assessment of biological and chemical agents against guava decline

ABSTRACT Guava decline is a complex disease resulting from the parasitism by Meloidogyne enterolobii (Me), which predisposes the plant to root rot caused by Fusarium sp. Three in vitro experiments were carried out with the aim of: (i) selecting the Fluensulfone dosage capable of causing Me mortality; (ii) verifying the effect of Fluensulfone on Pochonia chlamydosporia and Trichoderma harzianum; (iii) evaluating the effect of Pochonia chlamydosporia and Trichoderma harzianum in pure doses and in association with Fluensulfone on Me mortality. Fluensulfone at 2 L.ha-1 had no effect on fungi. The associated and pure doses of treatments had a significant effect on Me mortality. A field experiment was also carried out in a guava orchard where decline occurred. The following treatments were tested: Fluensulfone; P. chlamydosporia; P. chlamydosporia + Fluensulfone; T. harzianum; T. harzianum + Fluensulfone; Carbofuran, and control. All treatments reduced Me population, since relative efficiency was higher than 80%. Fluensulfone used alone or in combination with biological nematicides provided an increase in guava productivity. Maintaining Me population low in the field is an important option for increasing productivity and reducing the losses suffered by farmers.

Guava decline: updating its etiology from ‘Fusarium solani’ to Neocosmospora falciformis

Since the early 2000s, over 5000 hectares of guava orchards have been decimated in Brazil by guava decline. The disease has caused tens of millions of dollars in yield losses, the loss of thousands of jobs, and the closing of many fruit pulp-processing plants. Guava decline has been described as a synergistic interaction between the nematode Meloidogyne enterolobii and the fungus Fusarium solani. Nonetheless, the etiology of the disease has had to be reappraised because recent molecular studies have reassigned the whole ‘F. solani species complex’ to the genus Neocosmospora, with several plant-parasitic species being reclassified or synonymized. Hence, from a collection of ‘F. solani’ isolates associated with guava decline, we chose four of the most aggressive isolates, from which we sequenced RNA polymerase II subunit 1 (RPB1), RNA polymerase II subunit 2 (RPB2), and translation elongation factor 1-alpha (TEF1) genes. A GenBank® BLASTn search showed that the isolates belonged to Neocosmospora sp. Phylogenetic analyses using the maximum likelihood (ML) and Bayesian inference (BI) methods, with individual and combined datasets for TEF1, RPB1 and RPB2 genes, clustered all isolates within the N. falciformis clade, with maximum support in the ML and BI multilocus analyses. This and previous studies show that N. falciformis is the causal agent of guava decline and soybean sudden death syndrome, as well as of crown and root rots in other annual and perennial crops.

Guava seedlings with rootstocks or interstocks and their reaction to salinity

ABSTRACT The introduction of rootstocks for the guava has become necessary due to the advance of guava decline. Among them, Psidium spp. or their hybrids have been evaluated. In addition to disease resistance, tolerance to salinity must be evaluated in the new rootstocks. The aim of this study was to verify the effect of rootstocks and intergrafts on the mineral composition of Psidium spp. submitted to salt stress. The experiment was setup in a randomized block design, with the following treatments (scion/rootstock):P. guineense/P. cattleianum; P. guajava/P. guineense/P. cattleianum; P. guajava‘Paluma’/P. guajava; P. guajava ‘Paluma’/P. guineense; P. guajava ‘Cortibel 1’/P. guajava;P. guajava ‘Cortibel 1’/P. guineense; P. cattleianum (purple) and P. cattleianum (yellow), with three replications and three plants per plot. The plants underwent irrigation with saline solution, and the levels of macronutrients, micronutrients and sodium in the scion leaves were evaluated. As rootstock, P. cattleianum results in greater Na uptake, with higher levels in the leaves of the scions, leading to less tolerance to salt stress.

Emerging problem of guava decline caused by Meloidogyne enterolobii and Fusarium oxysporum f.sp. psidii

Guava orchards of district Ratlam were facing symptoms of sudden decline and loss in productivity due to heavy infestation of highly pathogenic species of root knot nematode, Meloidogyne enterolobii, not only by itself but also causing havoc through predisposing the host for secondary attack by wilt fungus Fusarium oxysporun f.sp. psidii causing disease-complex with synergistic effects on the common host guava (Cv VNR vihi). Wilted plants when uprooted showed numerous galls due to combined attack of both the vascular bundle feeders in stelar region of the host. Severely infested plant showed small leaves, leaf browning, leaf drop, growth inhibition whereas roots are distorted by small and large multiple galls leading to sudden death of tree.

Research on Fusarium wilt disease of guava

Wilting of guava trees has been regarded as national problem in India. Since, it is highly remunerative crop; disease is extremely important. The guava wilt was first reported in Taiwan during 1926 and in India during 1935. Several pathogenic fungi, nematodes and bacteria were found associated with the wilted trees of guava around the world; however, Fusarium spp. has been considered as major pathogen. Research on guava wilt carried out under network projects at ICAR-CISH revealed the cultural, morphological, molecular and pathogenic variability of Fusarium spp. across the India and its bio-management. Early age wilting of trees has mostly been observed due to complex of Fusarium oxysporum f. sp. Psidii, F. solani and Meloidogyne enterolobii. Enough research work on pathogenicity, cultural/morphological characters, molecular characterization, epidemiology and management of Fusarium spp. has been carried out but effect of interaction between Fusarium-Meloidogyne complex on expression of guava decline is yet to be thoroughly worked out. Complete guava crop management package should be developed, including healthy planting material production, proper care for nutrition, regular pruning and management of nematode fungus complex.

Selection of interspecific <i>Psidium</i> spp. hybrids resistant to <i>Meloidogyne enterolobii

Since 2001, the disease known as 'guava decline', resulting from the interaction between the phytonematode Meloidogyne enterolobii and the fungus Fusarium solanie, has caused direct and indirect economic losses to the entire guava production chain. Given the lack of sources of resistance in guava genotypes, interspecific hybrids of Psidium spp. were obtained for resistance to the nematode M. enterolobii. To classify the level of resistance of the interspecific hybrids, we evaluated the plant classification methodologies proposed by Oostenbrink (1966) and Moura and Régis (1987). Estimates of genetic parameters were obtained using the REML/BLUP approach. Interspecific hybrids resistant to M. enterolobii were selected that can be used as rootstocks or in new crosses for the development of the guava breeding program.

Influence of Natural Extracts Dipping to Maintenance Fruit Quality and Shelf Life of Egyptian Guava

Guava fruits are considered sensitive to low temperature and susceptible to infection by decay causing fungi making its transport and storability difficult. Use of plant extracts which having fungicidal and insecticidal properties is one of the alternative methods against fungi causing guava decline disease caused by Phomopsis psidii, Lasiodiplodia theobroma and Epicoccum spp. Therefore, the present investigations were conducted during 2016 and 2017 seasons on guava fruits cv. Bassateen El Sabahia for maintaining quality and control disease development under cold and ambient conditions. The guava fruits were harvested at physiological maturity stage during the third week of January and treated with marigold flower extract, neem extract and mentha leaf extract at (10%) as dip treatment for 5 minutes. (Experiment 1).Treated fruits were packed in ventilated Corrugated Fibre Board (CFB) boxes and stored 28 days under cold storage at 6° C ± 2° and humidity 90-95% R.H. (Experiment 2). The fruits were stored for 6 days in ambient conditions at 15° C ± 2° with 65 – 70 % R.H. Under both of the storage conditions, all treatments exhibit potential to maintain the postharvest life of fruits by reducing linear growth and dry weight of the fungal spoilage as compared with untreated fruits. The lowest significant values of disease infection percentage were recorded by dipping fruits in neem leaf extract at 10% after 28 days of cold storage and 6 days at marketing in the two seasons. Among all extracts, neem in combination with (CFB) boxes effective in registered higher potential to retain the fruit quality for longer period under both conditions by reducing the weight loss, fruit spoilage and retaining the fruit firmness and quality attributes such as TSS, sugars, vitamin C and pectin. On the other hand, 10% Mentha leaf extract followed by marigold flower extract treatments proved to be highly effective in reducing spoilage under these treatments with respect to the untreated ones. Generally, the promising effects of these treatments showed that the winter season guava fruits can be stored up to 28th day under cold storage and up to 6th day under ambient condition without deteriorating the fruit quality.

Reprodução do nematoide-das-galhas da goiabeira em acessos de Psidium

The guava decline, a complex disease caused by the interaction between Meloidogyne enterolobii and Fusarium solani, has caused damage to production and unviable guava producing areas in the Lower Basin of the São Francisco Valley. The management of this disease is difficult due to the facts that cultivated plants are susceptible to nematodes, nematicides have no effective control, and the use of fungicides to control Fusarium still has not been evaluated. However, some Psidium genotypes, such as the araçazeiros, show resistance to the nematodes, and therefore decline resistance. The objective of this study was to evaluate the interaction between genotypes of Psidium spp. and M. enterolobii to identify resistant plants. Three araçazeiro genotypes from the states of São Paulo and Paraná were artificially inoculated with M. enterolobii and compared with the species P. guajava cultivar Paluma, which is a commercial cultivar susceptible to root-knot nematode. All araçazeiro genotypes evaluated were resistant to the disease, with low reproduction factor (0.000 to 0.004) compared to cultivar Paluma (FR = 1,610). These results demonstrate that the araçazeiro genotypes have the potential to be used in the development of rootstocks resistant to guava decline.

Inheritance of resistance to Meloidogyne enterolobii and individual selection in segregating populations of Psidium spp

Interaction between the phytonematode Meloidogyne enterolobii and the fungus Fusarium solani has caused direct and indirect losses in the entire guava production chain and consequent extermination of guava plantations throughout Brazil. The combined action of these two pathogens is known as “guava decline”. In order to obtain and assess Psidium spp. interspecific hybrids for resistance to the nematode M. enterolobii, interspecific crosses of P. guineense (susceptible araca) x P. cattleyanum (resistant araca); P.guineense (susceptible araca) x P. guajava (susceptible guava) and P. cattleyanum (resistant araca) x P. guajava (susceptible guava) were conducted. These crosses resulted in hybrid immune, susceptible and resistant to Meloidogyne enterolobii. The chi-square test rejected the hypothesis of monogenic inheritance with incomplete dominance, which corroborates that this trait has polygenic action. Predictions of genetic values ​​and parameters were obtained by the REML / BLUP procedure, at individual level. Finally, the 30 selected individuals (immune and resistant) were obtained, which will be backcrossed with guava for the recovery of the agronomic traits desired and subsequent release of a new cultivar.

Relationships between M. enterolobii and F. solani: spatial and temporal dynamics in the occurrence of guava decline

Fil: del Valle, Eleodoro Eduardo. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe; Argentina

Relationships between M. enterolobii and F. solani: spatial and temporal dynamics in the occurrence of guava decline

Guava decline, caused by the interaction between the phytonematode Meloidogyne enterolobii and the fungus Fusarium solani, has caused direct and indirect losses to the whole productive chain of guava. Aiming to understand the interaction mechanisms between M. enterolobii and F. solani, this study carried out a bioassay on guava plants with roots in two different treatments: inoculated separatelyor together with the fungus and/or nematode. The nematode parasitism not triggered an systemic effect on the plant become susceptible to root rot caused by the fungus.Therefore, it was concluded that there was a local effect of parasitism by M. enterolobii on the pathogenicity of F. solani in guava roots, making it necessary for the two pathogens to occupy the same space at the same time for occurrence of guava decline.

Guava decline: effect of root exudates from Meloidogyne enterolobii-parasitized plants on Fusarium solani in vitro and on growth and development of guava seedlings under controlled conditions

In guava decline, Fusarium solani-immune guava trees become susceptible to extensive root rot caused by this fungus after parasitism by Meloidogyne enterolobii. To understand the mechanisms involved in this disease, root exudates were collected from nematode-inoculated (NI) or uninoculated (UN) guava plants cultivated in sand. After filtration through a Millipore® membrane, NI and UN exudates were used: i) to prepare media to assess their effect on mycelial growth and production of propagules of F. solani isolate UENF/CF 163, and ii) to incubate macro- and microconidia to assess their effect on germination. NI exudates promoted (P < 0.05) more mycelial growth and production of propagules than UN exudates or water. NI and UN exudates were used to water guava seedlings laid over seed germination paper inside plastic boxes. Half of the seedlings had an agar plug colonized by the fungus positioned in the collar region. Upon watering with NI exudates the fungus caused (P < 0.05) extensive rotting of the seedlings’ rootlets. NI and UN exudates, either unlyophilized or lyophilized and re-suspended to the original concentration, were used to water guava seedlings grown in sterile sand before being inoculated (or left uninoculated) as described before. Solely upon watering with NI exudates, in its unlyophilized form or after lyophilization, the fungus caused a reduction (P < 0.05) of shoot and root biomass associated with rotting of roots. These results suggest that M. enterolobii induces chemical changes in the root exudates of guava trees, which are necessary for root invasion causing root rotting by F. solani.

Greenhouse and field assessment of different organic compounds against guava-parasitic Meloidogyne enterolobii

Guava decline is a complex disease involving Meloidogyne enterolobii and Fusarium solani and it has caused major direct losses to Brazilian growers. Although several strategies have been sought to control the nematode, the use of organic soil amendments is currently the best approach to manage this disease. To assess the best amount of meat and bone meal (MBM) to be incorporated into the soil, guava seedlings inoculated with M. enterolobii were treated with 1-5% v/v of the MBM. Ninety days later variables related to nematode reproduction and plant development were evaluated, which indicated a potential nematicidal effect of the MBM at 3%. Another experiment assessed nematode- and plant-related variables 90 days after treatment of the seedlings with MBM, chitosan, shrimp shell or neem cake at 3%, 0.05%, 2% and 0.1% v/v, respectively. The MBM ranked first, reducing nematode reproduction. This MBM rate was converted to 25 kg/tree and assessed in three application regimes (monthly, bimonthly or trimonthly), for six months, in an orchard affected by guava decline. The variables assessed were soil density of colony forming units (CFU) of bacteria and fungus, and soil and/or root density of M. enterolobii, Helicotylenchus sp., and of different nematode trophic groups. In all three application regimes the MBM reduced all plant-parasitic nematodes in the soil and the fungus CFUs. It also promoted an increase in bacterial CFU and bacterivorous nematodes.

Greenhouse and field assessment of rhizobacteria to control guava decline

In an effort to devise a biological strategy to control guava decline, 120 rhizobacteria isolates were obtained from symptomless guava trees located in Meloidogyne enterolobii-infested orchards. Of those isolates, 44 were assessed for their potential to reduce nematode's reproduction: for each isolate, six guava stem cuttings were embedded for eight hours with bacterial suspension and transplanted. Upon development of the roots, the plants were inoculated with 2000 nematode eggs and allowed to grow for four months under greenhouse. Seedlings embedded with water, inoculated or not with the nematode, served as controls. All treatments were equivalent in the five variables that assessed plant development. Several rhizobacteria reduced (p&lt;0.05) the final nematode population (Fp), Fp/gram of root and reproduction factor, although not to satisfactory levels. Subsequently, a two-year experiment was set up in a guava orchard affected by guava decline, in which three of the most effective rhizobacterial isolates were compared with the biological products Nemat® and Nemaplus® for their ability to reduce variables related to nematode parasitism and increase guava productivity. Seven bimonthly applications of these treatments under the tree canopy were unable to reduce nematode parasitism and increase productivity. The decline and death of some plants forced the experiment to be stopped after the first harvest. In conclusion, rhizobacteria applications seem unable to reduce the parasitism of M. enterolobii on guava plants, and even less to reduce the extensive root decay or alleviate the physiological stress suffered by trees affected by guava decline.

Guava Decline: A Complex Disease Involving Meloidogyne mayaguensis and Fusarium solani

In Brazil, Meloidogyne mayaguensis has become a threat to guava production. Approximately a third of the cultivated area is infested, leading almost inevitably to the decimation of the orchards. Because parasitized trees develop rotten roots as the disease progresses, the possibility that a soil-borne pathogen could be involved was investigated. From several nematode-free or nematode-infested orchards, nearly 2000 root fragments were tested for bacteria and fungi. Positive isolations were obtained from nematode-infested areas only and were predominantly identified as Fusarium sp. In a 5-month microplot experiment, guava seedlings were uninoculated (control) or were inoculated with M. mayaguensis only or with this nematode and 21 days later with one of 11 Fusarium sp. isolates. A Scott–Knot analysis of several vegetative variables and of the extent of root rot allowed the generation of a dissimilarity dendrogram that indicated that four Fusarium sp. isolates were particularly associated with damage to the seedlings. Upon identification of these isolates as Fusarium solani, a 6-month microplot experiment was set up, in which guava seedlings were uninoculated or were inoculated with one of the following: (i) M. mayaguensis only, (ii) four F. solani isolates, separately, (iii) four F. solani isolates separately, combined with physical injury of the roots with a knife, (iv) M. mayaguensis, and 21 days later with four F. solani isolates, separately. No root rot and virtually no effect on all variables were observed in the seedlings inoculated with the fungus isolates, with or without physical injury. Major root rot and a negative effect on all variables were observed in the seedlings inoculated with M. mayaguensis and all four F. solani isolates. This characterizes guava decline as a complex disease caused by the synergistic effect of these organisms, in which parasitism by the nematode predisposes the plants to root decay caused by the fungus.