Rapid necrosis II: physiological and molecular analysis of 2,4-D resistance in Sumatran fleabane (Conyza sumatrensis)

In 2015, plants of Sumatran fleabane [Conyza sumatrensis (Retz.) E. Walker] were identified in a crop field with an unusual rapid necrosis herbicide symptom after application of 2,4-D. An initial study identified that the symptoms began about 2 h after herbicide application, the resistant factor is high (resistance factor = 19), and the resistance decreased at low light. The mechanism of resistance is not known yet, but the symptomatology suggests it may be related to reduced translocation, ATP-binding cassette class B (ABCB) transporters, changes on auxin perception genes or induction of genes involved in response to pathogens and abiotic stresses. The objective of this study was to investigate the mechanisms involved in the resistance to 2,4-D caused by rapid necrosis using inhibitors of enzymes involved in detoxification and carriers. Neither the inhibitors of ABCB and auxin transporters TIBA, NPA, verapamil and orthovanadate, nor the inhibitors of detoxifying enzymes, as malathion, NBD-Cl and imidazole, avoided the rapid necrosis phenotype. However, orthovanadate and sodium azide (possibly related with auxin transport) were able to partially reduce oxidative stress in leaf disc. The expression of ABCM10 (an ABCD transporter gene), TIR1_1 (an auxin receptor gene) and CAT4 (an amino acid transporter gene) was quickly reduced after 2,4-D application in the resistant accession. Contrary to our hypothesis, LESION SIMULATING DISEASE RESISTANCE 1_3 (LSD1_3) expression increased in response to 2,4-D. LSD1_3 is important for the response to pathogen and abiotic stresses. The rapid necrosis mechanism is not related to 2,4-D detoxification but might be related to changes in the TIR receptor or auxin transport. Mutations in other transporters or in proteins involved in abiotic and pathogen stresses cannot be ruled out.

Identification of new resistant sources against downy mildew disease from a selected set of cucumber germplasm and its wild relatives

This study was undertaken to identify new sources of resistance against downy mildew of cucumber caused by Pseudoperonospora cubensis [(Berk. and Cart.) Rostow]. Pot experiments were conducted with 16 accessions each of Cucumis sativus and C. hardwickii during the years 2017 and 2018 using 12 isolates of P. cubensis representing different agroclimatic zones of India. The accession, IC331627 from Dehradun, Uttarakhand showed plant disease index (PDI) ranging from 5.55-20.35 per cent with an average PDI of 11.56 and 11.87 per cent during the years, 2017 and 2018, respectively. Hence, IC331627 was identified to be resistant against the five isolates of P. cubesis (Pc12, Pc17, Pc19, Pc21 and Pc24) and moderately resistant against one isolate (Pc22). This resistant accession C. hardwickii (IC331627) could be utilized to develop mapping population to map genomic regions conferring the resistance to downy mildew in cucumber.

Dormancy breakage and germination are tightly controlled by hypoxic submergence water on Echinochloa crus-galli seeds from an accession resistant to anaerobic germination

In wetlands, dormancy may be a key functional trait enabling seeds to avoid underwater germination, which could be lethal for seedling establishment. Our objectives were to find out (i) if shallow dormant (i.e. conditionally dormant) Echinochloa crus-galli seeds from an anaerobic germination resistant accession can break dormancy under hypoxic submergence and (ii) if underwater germination can be restored in scarified, non-dormant seeds. Shallow dormant E. crus-galli seeds perceived diurnally alternating temperatures (AT) and red light (R) pulses (i.e. dormancy-breaking cues) under hypoxic submergence; however, an inhibitory far-red light pulse given at the end of the 4-d inundation period demonstrated that most of the seeds (85%) were unable to break dormancy. Scarified E. crus-galli seeds, which did not express dormancy under drained conditions, were unable to germinate under hypoxic submergence, despite being exposed to dormancy-breaking cues (AT + R). Lastly, the temporal window for germination sensitivity to the inhibitory action of hypoxia, once dormancy-breaking signals have been applied, is progressively lost and bounded to approximately 18 h for half of the seed lot. These results highlight the importance of dormancy as a trait enabling E. crus-galli seeds to avoid underwater germination, a risky scenario for seedling emergence and establishment in this facultative hydrophyte.

Oryza glumaepatula, a New Source of Resistance to Meloidogyne graminicola and Histological Characterization of Its Defense Mechanisms

Meloidogyne graminicola causes significant damage to rice fields worldwide. Sources of resistance to M. graminicola reported in Oryza sativa are limited. Resistance to this species has been found in other Oryza species such as O. glaberrima and O. longistaminata. This study aimed to evaluate the reaction of four wild species of Oryza from the Embrapa Rice and Bean Germplasm Bank (Goiás, Brazil) to a pool of M. graminicola populations and determine the resistance mechanism in O. glumaepatula. Two genotypes of O. glaberrima, one of O. alta, three of O. glumaepatula, one of O. grandiglumis, one of O. longistaminata, and one of O. sativa (control) were included in the study. The results showed that O. glumaepatula was highly resistant (reproduction factor [RF] < 1). O. glaberrima, O. alta, and O. grandiglumis were considered moderately resistant. O. longistaminata was susceptible, although values of RF remained lower than the control O. sativa ‘BR-IRGA 410’, considered highly susceptible. Histological observations on the interaction of O. glumaepatula and M. graminicola showed reduced penetration of second-stage juveniles (J2s) when this resistant wild accession was compared with O. sativa. An intense hypersensitivity response-like reaction occurred at 2 days after inoculation in the root cortex of the resistant accession. Few J2s established in the central cylinder, and rare collapsed giant cells were observed surrounded by degenerate females. Fluorescence microscopy in O. glumaepatula revealed giant cells and the female body presumably exhibiting accumulation of phenolic compounds. Our study suggests that wild rice accessions, especially from the AA genotype (e.g., O. glumaepatula), are of great interest for use in future breeding programs with Oryza spp.

Tingkat Ketahanan 70 aksesi Plasma Nutfah Kenaf terhadap Fusarium oxysporum Schletch; Assessment of Kenaf Germplasm Against Fusarium oxysporum Schletch

<p>Salah satu penyakit penting yang sangat merugikan tanaman kenaf adalah penyakit layu Fusarium yang disebabkan oleh <em>Fusarium oxysporum</em> Schlecht. Tujuan penelitian ini adalah untuk mengevaluasi tingkat ketahanan aksesi kenaf terhadap jamur <em>Fusarium oxysporum</em>. Penelitian dilakukan di laboratorium dan rumah kasa Balai Penelitian Tanaman Pemanis dan Serat, Malang menggunakan rancangan acak lengkap) yang diulang tiga kali. Dalam evaluasi ini digunakan 70 aksesi dan 1 aksesi tahan (BG-52-135) yang digunakan sebagai kontrol. Inokulasi dilakukan pada 7 hari setelah tanam (HST) menggunakan suspensi spora dengan kerapatan10⁵/ml sebanyak 100 ml setiap bak. Pengamatan intensitas serangan dilakukan mulai 10–40 hari setelah inokulasi (HSI) dengan interval pengamatan lima hari. Pengamatan persentase diskolorisasi batang dilakukan sekali pada 50 HSI. Hasil pengujian memperoleh 1 aksesi (FJ/017) sangat tahan dengan intensitas serangan terrendah (0,83%) dan 14 aksesi tahan dengan intensitas serangan <span style="text-decoration: underline;">&lt;</span>10%, 28 aksesi dengan ketahanan moderat, dan 27 aksesi yang rentan terhadap infeksi <em>F. oxysporum</em>. Aksesisi FJ/017 (aksesi yang sangat tahan) dan 14 aksesi yang tahan: 1064(SUC/012), 1061(SRB/082), 1035(FJ/005), 839(PARC/2709), 955(FJ/003), 842(PARC/2712), 1095(SUC/003), 838(PARC/2708), 957(FJ/ 007), 1065(SUC/023), 1042(CHN/056), 145(BL/118), 1036(FJ/006), dan 778(PARC/2466) dapat digunakan sebagai sumber ketahanan pada perakitan varietas baru.</p><p> </p><p>One of the important disease that very detrimental to kenaf is Fusarium wilt caused by <em>Fusarium oxysporum</em> Schlecht. The purpose of this study was to evaluate the response of 70 kenaf germplasm<span style="text-decoration: line-through;">s</span> accessions against <em>F</em><em>.</em><em> oxysporum</em>. The study was conducted at the Phytopatology Laboratory and screen house of Indonesian Sweetener and Fiber Crops Research Institute, Malang using completely randomized design with three replicates. Seventy accessions and one resistant accession as control (1267 (BG-52-135) were used in this study. Inoculation of <em>Fusarium</em> was done 7 days after sowing (das) by sprinkling 100 ml of spore suspension into the soil. Observation of disease intensity started at 10–40 days after inoculation (dai) and repeated every five days. Percentage of stalk discolorization was estimated at 50 dai. The results showed that accession 1040 (FJ/017) had the lowest disease intensity (0.83%), hence was categorized as a highly resitant accession. Fourteen accessions were categorized as resistant with disease intensity below or equal to 10%; 28 accessions were moderate resistant; and 27 accessions were susceptible. FJ/017 (the highset resistant accession) and 14 resis-tant accessions (1064(SUC/012), 1061(SRB/082), 1035(FJ/005), 839(PARC/2709), 955(FJ/003), 842(PARC/ 2712), 1095(SUC/003), 838PARC/2708), 957(FJ/007), 1065(SUC/023), 1042(CHN/056), 145(BL/118), 1036 (FJ/006), dan 778(PARC/2466)) could be used as resistant genetic sources in developing new varieties.</p>

Ketahanan Aksesi Kapas terhadap Hama Pengisap Daun, Amrasca biguttula (ISHIDA)

<p>Amrasca biguttula (Ishida) adalah salah satu hama utama kapas di Indonesia. Nimfa dan dewasanya meru-sak dengan cara mengisap cairan daun yang menyebabkan gejala seperti terbakar, kekeringan, dan gugur. Pengendalian hama ini semakin sulit karena terjadinya resistensi dan resurgensi hama akibat penggunaan insektisida kimia sintetis yang kurang bijaksana. Berkaitan dengan ketahanan terhadap A. biguttula, karakter morfologi tanaman kapas, khususnya trikom daun memegang peranan penting dalam mekanisme ketahan-an. Penelitian ini bertujuan untuk memperoleh aksesi-aksesi kapas yang tahan terhadap A. biguttula. Pene-litian evaluasi ketahanan plasma nutfah kapas terhadap A. biguttula (Ishida) dilakukan di KP Asembagus, Si-tubondo, mulai Januari hingga Desember 2008. Sebanyak 50 aksesi kapas digunakan sebagai perlakuan yang disusun dalam rancangan acak kelompok (RAK), dengan tiga kali ulangan. Ukuran plot perlakuan 10 m x 3 m, dengan jarak tanam 100 cm x 25 cm, satu tanaman per lubang. Parameter yang diamati adalah: po-pulasi nimfa A. biguttula, tingkat kerusakan tanaman, dan karakter trikom daun yang meliputi: kerapatan, panjang, dan posisi trikom. Hasil penelitian menunjukkan bahwa kerapatan trikom daun berhubungan de-ngan ketahanan terhadap A. biguttula. Aksesi dengan kerapatan trikom daun yang tinggi lebih tahan ter-hadap serangan A. biguttula dibanding aksesi dengan sedikit trikom atau tidak bertrikom. SK 32, LAXMI, dan SK 14 adalah aksesi kapas yang tahan terhadap serangan A. biguttula, sedangkan SATU 65, LASANI 1, G-cot-10, SAMARU 70, NH4, L 18, dan NIAB adalah aksesi-aksesi dengan tingkat ketahanan sedang (moderat). Selain itu, aksesi yang termasuk sangat rentan adalah: Stoneville 825, 7042-5W-79N, 1073-16-6x491L-619-4-77, dan M35-5-8, sementara aksesi lainnya termasuk rentan terhadap serangan. Terdapat korelasi negatif antara kerapatan trikom daun dan populasi nimfa (Y=-170,8x + 296,6; R2 = 0,414) dan antara kerapatan trikom daun dan tingkat/skor kerusakan tanaman (Y=-0,005x + 2,916; R2 = 0,622). Se-dangkan korelasi positif terjadi antara populasi nimfa dan tingkat/skor kerusakan tanaman (Y=0,469x – 0,071; R2 = 0,672).</p><p> </p><p>The cotton jassid, Amrasca biguttula (Ishida) is a key pest of cotton in Indonesia. The nymphs and adults suck the leaves resulting in hopperburn, drying, and shedding of leaves. The management of this pest is more difficult due to the insect resistance to chemical insecticides and resurgence caused by unwise applications of synthetic insecticides. Related to jassid resistance, morphology of cotton mainly hairiness of leaf, plays an important role in mechanism on the plant resistance. The objective of the study was to screen a large number of cotton accessions for susceptible or resistant to A. biguttula. The study was conducted at Asembagus Experimental Station from January to December 2008. Fifty accessions of cotton were planted in 10 m x 3 m of plot size with 100 cm x 25 cm of plant distance. All accessions were designed in randomized block with three replications. Each plot consists of two rows cotton accession and one row susceptible varie-ty, TAMCOT SP 37 as a attractant plant. Parameters observed were nymph population, plant damage, tri-chome characters and its density, length, and position on the leaf lamina. Results showed that cotton acces-sions with higher trichome density were more resistant to jassid compared to the less trichome of accession. SK 32, LAXMI, and SK 14 were more resistant accession to A. biguttula, while SATU 65, LASANI 1, G-cot-10, SAMARU 70, NH4, L 18, and NIAB were categorized as intermediate resistant accessions to the pest. Sto-neville 825, 7042-5W-79N, 1073-16-6x491L-619-4-77, and M35-5-8 were found as the most susceptible to A. biguttula. Negative correlation was occured between trichome density and nymph population (Y=-170,8x + 296,6; R2 = 0,414) and between trichome density and damage score (Y=-0,005x + 2,916; R2 = 0,622), while positive correlation was found between nymph population and damage score (Y=0,469x – 0,071; R2 = 0,672).</p>

Identification and characterisation of resistance to the cereal cyst nematode Heterodera filipjevi in winter wheat

The aim of this study was to search for new sources of resistance against the cereal cyst nematode,Heterodera filipjevi, in a collection of 290 wheat accessions. The plants were inoculated with juveniles and assessed for the number of females and cysts. One percent of the wheat accessions were ranked as resistant, 16% as moderately resistant, 41% as moderately susceptible, 26% as susceptible and 15% as highly susceptible. The infection rate and the number of females and cysts per plant were significantly lower in the resistant accession Nudakota and three moderately resistant accessions Ekonomka, Katea and Lantian 12 compared with susceptible cv. Bezostaya 1. Nematode development was reduced in resistant and moderately resistant accessions. The size of females and the total number of eggs and second-stage juveniles were reduced only in Ekonomka. No significant difference in plant height, plant weight, root length, root weight and root volume were recorded for inoculated plants compared to non-inoculated plants. This study has identified four resistant wheat accessions offering new material for breeding the resistance toH. filipjevi.

Inheritance of Resistance to Powdery Mildew Race 1W in Watermelon

Powdery mildew caused by Podosphaera xanthii is a major disease of watermelon in Israel. In this study, 291 accessions of Citrullus spp. were evaluated for resistance against P. xanthii race 1W. Only eight accessions exhibited high level of resistance. Inheritance of resistance against P. xanthii race 1W was studied by crossing three resistant accession of Citrullus lanatus var. citroides BIU 119, PI 189225, or PI 482312 with the susceptible cultivar ‘Malali’ or ‘Sugar Baby’. Parents, F1, F2, and back cross progenies were evaluated for resistance in growth chambers at the cotyledon stage and the 4-leaf stage and in the field, at the 15-leaf stage. Resistance at the cotyledon stage was controlled by a single, partially dominant gene, whereas at the 4-leaf stage or the 15-leaf stage resistance was controlled by three complimentary, partially dominant genes. Crosses made among these resistant accessions revealed that BIU 119 and PI 189225 carry the same genes for resistance, whereas PI 482312 shares two out of three genes with both BIU 119 and PI 189225. A breeding line with high resistance level and good fruit qualities was developed from BIU 119 × HA5500.

Noncompetitive Growth and Fecundity of Wisconsin Giant Ragweed Resistant to Glyphosate

Glyphosate-resistant giant ragweed has been confirmed in several Midwestern states. In some cases, weed resistance to glyphosate has been shown to carry a fitness penalty. Previous research has found that a glyphosate-resistant giant ragweed biotype from Indiana with a rapid necrosis response to glyphosate displayed early, rapid growth in the absence of glyphosate, flowered earlier, but produced 25% less seed than a sensitive biotype, suggesting that there may be a fitness penalty associated with the rapid necrosis resistance trait. In Wisconsin, we have recently identified a giant ragweed accession with a 6.5-fold level of resistance to glyphosate that does not demonstrate the rapid necrosis response. Our objective was to determine the noncompetitive growth and fecundity of the resistant accession in the absence of glyphosate, relative to a sensitive accession from a nearby field border population. In greenhouse experiments, plant height, leaf area, and dry shoot biomass were similar between the resistant and sensitive accessions during vegetative growth to the onset of flowering. The instantaneous relative growth rate, instantaneous net assimilation rate, and instantaneous leaf area ratio also did not differ between accessions. However, fecundity of resistant plants (812 seeds plant−1) was greater (P = 0.008) than sensitive plants (425 seeds plant−1). The percentage of intact viable seeds, intact nonviable seeds, and empty involucres did not differ between resistant and sensitive accessions. These results indicate that resistance of this accession of giant ragweed to glyphosate has not affected its growth and development relative to a sensitive accession. The greater fecundity and similar viability of resistant plants relative to sensitive plants suggests that in the absence of selection by glyphosate, the frequency of the resistance trait for glyphosate may increase in the giant ragweed field population over time.

Response of Nebraska Kochia (Kochia scoparia) Accessions to Dicamba

Kochia is a troublesome weed in the western Great Plains and many accessions have evolved resistance to one or more herbicides. Dicamba-resistant soybean is being developed to provide an additional herbicide mechanism of action for POST weed control in soybean. The objective of this study was to evaluate variation in response to dicamba among kochia accessions collected from across Nebraska. Kochia plants were grown in a greenhouse and treated when they were 8 to 12 cm tall. A discriminating experiment with a single dose of 420 g ae ha−1of dicamba was conducted on 67 accessions collected in Nebraska in 2010. Visual injury estimates were recorded at 21 d after treatment (DAT) and accessions were ranked from least to most susceptible. Four accessions representing two of the most and least susceptible accessions from this screening were subjected to dose-response experiments using dicamba. At 28 DAT, visible injury estimates were made and plants were harvested to determine dry weight. An 18-fold difference in dicamba dose was necessary to achieve 90% injury (I90) between the least (accession 11) and most susceptible accessions. Approximately 3,500 g ha−1of dicamba was required in accession 11 to reach a 50% dry weight reduction (GR50). There was less than twofold variation among the three more susceptible accessions for both the I90and GR90parameters, suggesting that most kochia accessions will be similarly susceptible to dicamba. At 110 DAT, accession 11 had plants that survived doses of 35,840 g ha−1, and produced seed at doses of 17,420 g ha−1. The identification of one resistant accession among the 67 accessions screened, and the fact that dicamba doses greater than 560 g ha−1were required to achieve GR80for all accessions suggest that repeated use of dicamba for weed control in fields where kochia is present may quickly result in the evolution of dicamba-resistant kochia populations.