IDENTIFICATION OF SOURCES OF RESISTANCE TO Meloidogyne enterolobii IN ACEROLA1

ABSTRACT In Brazil, acerola trees infested by Meloidogyne enterolobii present lower yield and fruit quality. The use of rootstocks resistant to this pathogen is one of the alternatives to overcome this problem. This study aimed to assess the reaction of 22 acerola accessions to M. enterolobii, aiming to identify at least one resistant rootstock. The experiment was carried out in a randomized block design with 10 replications and each plot consisting of 10 plants. Each plant was inoculated with 350 eggs and second-stage juveniles of M. enterolobii, with the gall index (GI) and reproduction factor (RF) being determined after 90 days. The variables were analyzed using the mixed model methodology (REML/BLUP). The accessions ACO-13, ACO-14, ACO-18, and BRS Apodi stood out with four to six plants showing resistance reaction to the root-knot nematode, but the assessment of accessions should be performed under a higher density inoculum and longer time.

Cytological Studies on Graft Union Development with Perennial Chilli Rootstocks

Grafting technology in vegetable crops is becoming increasingly popular as an alternative tool to improve the biotic and abiotic resistance besides improvement in horticultural traits. By utilizing the right combination of resistant rootstock and scion, desired variability can be achieved to improve the yield and quality of vegetables. A study was conducted at the College orchard, Department of Vegetable science, Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore during the year 2020-2021 to evaluate the graft compatibility with two chilli rootstocks. The experimental material consisted of two perennial rootstocks viz., CC-CBE-001 and CF-CBE-007 and three scion materials viz., TNAU Chilli Hybrid CO 1, Ranga hybrid and Bangaram hybrid. Wedge grafting was done using 60 days old rootstock and 45 days old scion seedlings with nine treatments. The adhesion line wall thickness of pith cells were determined at different stages after grafting. The wound healing of the scion-rootstock union was studied using microscopic examination of the grafting region on the 5th, 10th, 15th and 20th day after grafting. It was observed that ten days after grafting, vascular bundle was formed and a large amount of callus was produced to bridge the scion and rootstock. Despite interspecific grafting, callus formation, subsequent cell differentiation and vascular connection were established, resulting in effective graft compatibility, according to the anatomical and histological analysis.

Defense Response to Hemileia vastatrix in Susceptible Grafts onto Resistant Rootstock of Coffea arabica

The use of resistant cultivars and fungicides are common methods to control coffee leaf rust (CLR), the main disease that affects the Arabica coffee crop. In this study, we evaluated the response of grafted and ungrafted plants during the early stage of Hemileia vastatrix infection. We used ungrafted plants of Oro Azteca (resistant cultivar) and Garnica (susceptible cultivar), and grafted plants, combining both as rootstock and graft (Garnica/Oro Azteca and Oro Azteca/Garnica). All plants were inoculated with H. vastatrix uredospores, and we quantified the development of fungal structures in the leaf tissue of inoculated plants using qRT-PCR to measure relative expression of two pathogenesis recognition genes (CaNDR1 and CaNBS-LRR) and three genes associated with the salicylic acid (SA) pathway (CaNPR1, CaPR1 and CaPR5). In Garnica grafted on Oro Azteca, the fungal structures recorded were significantly less than in Garnica ungrafted plants. In addition, the expression of defense-related genes in grafted plants was higher than in ungrafted plants. Our results indicate that the defense response to CLR is strongly influenced by the rootstock employed.

Pengaruh Tomat Sambung Pada Intensitas Penyakit Layu Bakteri (Ralstonia solanacearum), Komponen Hasil Produksi, dan Kualitas Buah

Ralstonia solanacearum (Smith) is one of soil borne pathogens causes bacterial wilt diseases and R. solanacearum is difficult to control because it has a long survival in the soil and have many hosts alternatives. One alternative to control R. solanacearum and to increase productivity is by using grating with combination of resistant varieties of tomato as a rootstock and high production varieties of tomato as a scion. Several studies on grafting to suppress R. solanacearum were reported. However, study on grafting with combination between resistant tomato varieties (Amelia H7996) and high-production tomato varieties with R. solanacearum infestation and without R. solanacearum infestation on the component of yield and fruit quality is limited. The study aims to analyze the effect of grafting with R. solanacearum infestation to the intensity of bacterial wilt disease, component of yield, and fruit quality with R. solanacearum infestation and without R. solanacearum infestation. The result indicated that the intensity of bacterial wilt disease on grafted tomato did not significantly different from resistant rootstock but significantly different from scion. Infestation of R. solanacearum on grafted tomato can decreased the plant productivity that decreased the component of yield on grafted tomato. R. solanacearum infestation also decreased the fruit quality on diameters and fruit firmness. Nevertheless, R. solanacearum did not affect the Total soluble solid/TSS (°Brix). TSS on grafted tomato indicated that the value is taller than rootstock in the field with R. solanacearum infestation and in the field without R. solanacearum infestation. Keywords: fruit quality, productivity, Rasltonia solanacearum, tomato grafted

Effect of Grafting on Viral Resistance of Non-transgenic Plum Scion Combined With Transgenic PPV-Resistant Rootstock

In stone fruit trees, resistance to Plum pox virus (PPV) can be achieved through the specific degradation of viral RNA by the mechanism of RNA interference (RNAi). Transgenic virus-resistant plants, however, raise serious biosafety concerns due to the insertion and expression of hairpin constructs that usually contain various selective foreign genes. Since a mature stone tree represents a combination of scion and rootstock, grafting commercial varieties onto transgenic virus-tolerant rootstocks is a possible approach to mitigate biosafety problems. The present study was aimed at answering the following question: To what extent are molecular RNAi silencing signals transmitted across graft junctions in transgrafted plum trees and how much does it affect PPV resistance in genetically modified (GM)/non-transgenic (NT) counterparts? Two combinations, NT:GM and GM:NT (scion:rootstock), were studied, with an emphasis on the first transgrafting scenario. Viral inoculation was carried out on either the scion or the rootstock. The interspecific rootstock “Elita” [(Prunus pumila L. × P. salicina Lindl.) × (P. cerasifera Ehrh.)] was combined with cv. “Startovaya” (Prunus domestica L.) as a scion. Transgenic plum lines of both cultivars were transformed with a PPV-coat protein (CP)-derived intron-separate hairpin-RNA construct and displayed substantial viral resistance. High-throughput sequence data of small RNA (sRNA) pools indicated that the accumulation of construct-specific small interfering RNA (siRNA) in transgenic plum rootstock reached over 2%. The elevated siRNA level enabled the resistance to PPV and blocked the movement of the virus through the GM tissues into the NT partner when the transgenic tissues were inoculated. At the same time, the mobile siRNA signal was not moved from the GM rootstock to the target NT tissue to a level sufficient to trigger silencing of PPV transcripts and provide reliable viral resistance. The lack of mobility of transgene-derived siRNA molecules was accompanied by the transfer of various endogenous rootstock-specific sRNAs into the NT scion, indicating the exceptional transitivity failure of the studied RNAi signal. The results presented here indicate that transgrafting in woody fruit trees remains an unpredictable practice and needs further in-depth examination to deliver molecular silencing signals.

In vitro co-culture system for Prunus spp. and Armillaria mellea in phenolic foam rooting matric

Armillaria and Desarmillaria spp. are causal agents of a devastating root-borne disease of peach. Breeding resistant rootstock requires a reliable screening tool. An in vitro co-culture screen designed for almond was modified by replacing agar-gelled medium with a more aerated phenolic foam and combining resistant and susceptible rootstocks (i.e., common garden experiment) and minimizes variation in inoculum pressure or rooting substrate among replicate vessels. Eight Prunus rootstocks tested (peach, plum, peach × plum, and choke cherry) were rooted and had no decline in health. Susceptible peach rootstock, ‘GF 305’, was cultured for 15 wk in phenolic foam in the same vessel with a resistant peach × plum hybrid, ‘MP-29’, inoculated with Armillaria mellea at week 5, that led to more severe shoot symptoms in the former after an additional 8 wk. This method accommodated peach genotypes that were difficult to root in agar medium. The difference during a uniform challenge with the A. mellea fungus recapitulates resistant/susceptible reactions. The phenolic foam-based co-culture method will work on many Prunus spp. of potential use in rootstock breeding.

Development of in vitro culture establishment conditions and micropropagation of grapevine rootstock cultivar ‘Ruggeri-140’

Optimization of in vitro culture conditions of grapevine phylloxera-resistant rootstock cultivar ‘Ruggeri-140’(Vitisberlandieri x Vitisrupestris) was carried out. Among the different sterilization treatments, maximum aseptic cultures were obtained for both explants apical tips and nodal segments when treated with Ca(ClO)2 at concentration of 1.5 % for 10 minutes plus 70 % ethanol for 30 s (T7). The maximum shoot proliferation was observed both in apical and nodal meristems cultured on MS medium supplemented with 1.0 mg/l BAP. MS/2 medium containing 1.0 mg/l indole-3-butric acid (IBA) gave the highest rooting percentage (100%) with the highest mean number and length of roots. The ex vitro survival of rooted micro shoots was 75.0%.

Rootstock-Scion Interaction Affects the Composition and Pathogen Inhibitory Activity of Tobacco (Nicotiana tabacum L.) Root Exudates

The composition and allelopathy to Phytophthora nicotianae (the causal agent of tobacco black shank disease) of root exudates from a resistant tobacco (Nicotiana tabacum L.) cultivar Gexin 3, a susceptible cultivar Xiaohuangjin 1025 and their reciprocal grafts were investigated. Grafting with disease-resistant rootstock could improve resistance to black shank; this is closely related to the allelopathy of root exudates. The root exudates from the resistant cultivar inhibited the growth of P. nicotianae, while those from the susceptible cultivar promoted the growth; the grafting varieties had intermediate properties. The root exudate composition differed among cultivars. Gexin 3 was rich in esters and fatty acids, while Xiaohuangjin 1025 contained more hydrocarbons and phenolic acids. The composition of root exudates of grafted cultivars as well as their allelopathy to P. nicotianae were altered, and tended to be close to the composition of cultivar used as rootstock. Eugenol, 4-tert-butylphenol, mono (2-ethylhexyl) phthalate, 4-hydroxybenzoic acid, 2,6-di-tert-butylphenol, dipropyl phthalate, and methyl myristate were identified as the main compounds contributing to inhibitory properties of root exudates. Sorbitol was suggested to play a role in disease induction. Overall, rootstock–scion interaction affected the composition of tobacco root exudates, which may be attributed to the different disease resistance among grafted plants, rootstock and scion.

Suppressing Bacterial Wilt (Ralstonia solanacearum) by Grafting Tomato Seedlings Grown on Six Comparable Media

Bacterial wilt caused by Ralstonia solanacearum is an important disease of tomatoes. The grafting method with a resistant rootstock variety is a reliable control technique and has been carried out in many countries. Healthy tomato seedling are needed for grafting so this study was aimed to find a good seedling medium to grow the upper stem and rootstock of tomato for grafting and to know the effect of seed media on the intensity of bacterial wilt). Tomato seeds were grown in coir and rice husk charcoal with ratio A (10:0), B (9:1), C (8:2), D (7:3), E (6:4), F (5:5) (coir : rice husk charcoal, v/v). Seedlings were watered regularly and after seedlings aged 21 days, the grafting was conducted. Agronomic observations were justified by measuring germination style, plant height, leaf area, fresh mass and dry mass of plants at 21 days after planting. Tomato seedlings were grafted by using H-7996 variety as a rootstock and Servo variety as an upper stem. Tomato seedlings were transplanted into polybags and then inoculated with R. solanacearum (108 CFU/ml). The disease intensity and AUDPC (Area Under Disease Progress Curve) were recorded. The results revealed that the media with a ratio of 8:2 (coir : rice husk charcoal, v/v) is the best medium for growing tomatoes and the grafting treatment could reduce the disease intensity of bacterial wilt by 40% compared with non grafted treatment and reduce 16% disease intensity compared to the grafted treatment with seedling sown in other ratio media at the last observation.