Identification of Glucosinolates in Seeds of Three Brassicaceae Species Known to Hyperaccumulate Heavy Metals

Plants from the Brassicaceae family are known to contain secondary metabolites called glucosinolates. Our goal was to establish by LC/MS the glucosinolate profile of seeds of three Brassicaceae species known to hyperaccumulate heavy metals. We investigated Alyssum fallacinum auct. non Hausskn ., Iberis intermedia Guers ., and Noccaea caerulescens (J. Presl & C. Presl ) F. K. Mey . Our results indicate that A. fallacinum seeds contain glucoiberin and glucoibervirin, which had not been previously identified in this plant. Furthermore, we report for the first time the presence of glucoiberin, glucoibervirin, glucotropaeolin, and sinigrin in I. intermedia. We have detected for the first time glucoconringiin in N. caerulescens. In addition, glucosinalbin, 4‐hydroxyglucobrassicin, and glucomoringin were also detected.     

Valuable New Resistances Ensure Improved Management of Sclerotinia Stem Rot (Sclerotinia sclerotiorum) in Horticultural and Oilseed Brassica Species

Field resistances against Sclerotinia rot (SR) (Sclerotinia sclerotiorum) were determined in 52 Chinese genotypes of Brassica oleracea var. capitata, 14 Indian Brassica juncea genotypes carrying wild weedy Brassicaceae introgression(s) and four carrying B‐genome introgression, 22 Australian commercial Brassica napus varieties, and 12 B. napus and B. juncea genotypes of known resistance. All plants were individually inoculated by securing an agar disc from a culture of S. sclerotiorum growing on a glucose‐rich medium to the stem above the second internode with Parafilm tape. Mean stem lesion length across tested genotypes ranged from <1 to >68 mm. While there was considerable diversity within the germplasm sets from each country, overall, 65% of the B. oleracea var. capitata genotypes from China showed the highest levels of stem resistance, a level comparable with the highest resistance ever recorded for oilseed B. napus or B. juncea from China or Australia. One Indian B. juncea line carrying weedy introgression displayed a significant level of both stem and leaf resistance. However, the vast majority of commercial Australian oilseed B. napus varieties fell within the most susceptible 40% of genotypes tested for stem disease. There was no correlation between expressions of stem versus leaf resistance, suggesting their independent inheritance. A few Chinese B. oleracea var. capitata genotypes that expressed combined extremely high‐level stem (≤1 mm length) and leaf (≤0.5 mean number of infections/plant) resistance will be particularly significant for developing new SR‐resistant horticultural and oilseed Brassica varieties.     

Genetic changes in a novel breeding population of Brassica napus synthesized from hundreds of crosses between B. rapa and B. carinata

Introgression of genomic variation between and within related crop species is a significant evolutionary approach for population differentiation, genome reorganization and trait improvement. Using the Illumina Infinium Brassica 60K SNP array, we investigated genomic changes in a panel of advanced generation new‐type Brassica napus breeding lines developed from hundreds of interspecific crosses between 122 Brassica rapa and 74 Brassica carinata accessions, and compared them with representative accessions of their three parental species. The new‐type B. napus population presented rich genetic diversity and abundant novel genomic alterations, consisting of introgressions from B. rapa and B. carinata, novel allelic combinations, reconstructed linkage disequilibrium patterns and haplotype blocks, and frequent deletions and duplications (nonrandomly distributed), particularly in the C subgenome. After a much shorter, but very intensive, selection history compared to traditional B. napus, a total of 15 genomic regions with strong selective sweeps and 112 genomic regions with putative signals of selective sweeps were identified. Some of these regions were associated with important agronomic traits that were selected for during the breeding process, while others were potentially associated with restoration of genome stability and fertility after interspecific hybridization. Our results demonstrate how a novel method for population‐based crop genetic improvement can lead to rapid adaptation, restoration of genome stability and positive responses to artificial selection.     

Pre‐ and post‐ingestive defenses affect larval feeding on a lethal invasive host plant

Evolutionary traps arise when organisms use novel, low‐quality or even lethal resources based on previously reliable cues. Persistence of such maladaptive interactions depends not only on how individuals locate important resources, such as host plants, but also the mechanisms underlying poor performance. Pieris macdunnoughii (Remington) (Lepidoptera: Pieridae) lays eggs on a non‐native mustard, Thlaspi arvense (L.) (Brassicaceae), which is lethal to the larvae. We first tested whether larval feeding behavior was affected before (pre‐) ingestion or following (post‐) ingestion of leaf material, indicating activity of feeding deterrents, toxins, or both in this evolutionary trap. Neonates were less likely to start feeding and eventually fed more slowly on T. arvense than on the native host plant Cardamine cordifolia (Gray) (Brassicaceae) in both laboratory and field. Starvation was a primary cause of mortality, indicating the role of a feeding deterrent. Feeding did not differ between larvae from invaded and uninvaded population. Second, T. arvense defensive chemistry is dominated by the glucosinolate sinigrin (allyl or 2‐propenyl glucosinolate). Adding sinigrin to the leaves of T. arvense and native hosts C. cordifolia and Descurainia incana (Bernhardi ex Fischer & Meyer) (Brassicaceae) delayed the onset of feeding, caused larvae to feed more slowly, and decreased survival on the native hosts. This evolutionary trap may not be driven by a novel deterrent, but rather by a change in the concentration of a deterrent found in native hosts. Many insects have adapted to evolutionary traps posed by invasive plants, incorporating the new plant into their diets. Thlaspi arvense remains lethal to P. macdunnoughii, and pre‐ingestive deterrents such as excess sinigrin may contribute to persistent maladaptation.     

A quartet pollen phenotype identified in a population of Brassica interspecific hybrids shows incomplete penetrance and variable response to temperature

• Quartet pollen, where pollen grains remain attached to each other post‐meiosis, is useful for tetrad analysis, crossover assessment and centromere mapping. We observed the quartet pollen phenotype for the first time in the agriculturally significant Brassica genus, in an experimental population of allohexaploid Brassica hybrids derived from the cross (Brassica napus × B. carinata) × B. juncea followed by two self‐pollination generations.
• Quartet pollen production was assessed in 144 genotypes under glasshouse conditions, following which a set of 16 genotypes were selected to further investigate the effect of environment (warm: 25 °C and cold: 10 °C temperatures) on quartet pollen production in growth cabinets.
• Under glasshouse phenotyping conditions, only 92 out of 144 genotypes produced enough pollen to score: of these, 30 did not produce any observable quartet pollen, while 62 genotypes produced quartet pollen at varying frequencies. Quartet pollen production appeared quantitative and did not clearly fall into phenotypic or qualitative categories indicative of major gene expression. No consistent effect of temperature on quartet pollen production was identified, with some genotypes producing more and some producing less quartet pollen under different temperature treatments.
• The genetic heterogeneity and frequent pollen infertility of this population prevents strong conclusions being made. However, it is clear that the quartet phenotype in this Brassica population does not show complete penetrance and shows variable (likely genotype‐specific) response to temperature stress. In future, identification of quartet phenotypes in Brassica would perhaps best be carried out via screening of diploid (e.g. B. rapa) TILLING populations.

     

Survival of Phytophthora cinnamomi and Fusarium verticillioides in commercial potting substrates for ornamental plants

Live plants, particularly when accompanied by soil or potting substrates, are considered the main pathway for international spread of plant pathogens. Modern, rapid shipping technologies for international plant trade increase the probability of plant pathogen survival during transport and the subsequent chances of disease outbreaks in new locations. The survival of two model pathogens, an Oomycete, Phytophthora cinnamomi, and a filamentous fungus, Fusarium verticillioides, was studied in two different commercial potting substrates (peat and peat‐free) under glasshouse conditions in the absence of a plant host. Survival rates were analysed at 2, 7, 12 and 17 months after substrate inoculation. Fusarium verticillioides had the longest survival rate, and was still present at 17 months. In contrast, P. cinnamomi survived up to 7 months but was not recovered after 12 or 17 months. There was no significant difference in the number of colony‐forming units (CFUs) of either pathogen in the two substrates, except at 2 months, when higher numbers were recovered from peat substrates.     

‘Myrosin cells’ are not a prerequisite for aphid feeding on oilseed rape (Brassica napus) but affect host plant preferences

The enzyme myrosinase (EC 3.2.3.1.147) is present in specialised myrosin cells and forms part of the glucosinolate–myrosinase system, also known as ‘the mustard oil bomb’, which has an important role in the defence system of cruciferous plants against insect pests. Transgenic Brassica napus MINELESS have been produced by transgenic ablation of myrosin cells. This prompted us to investigate the importance of myrosin cells in plant–aphid interactions. In order to study this, we challenged transgenic MINELESS and wild‐type cultivar Westar seedlings with the aphids Brevicoryne brassicae (a specialist) and Myzus persicae (a generalist). Our study included aphid free‐choice and aphid fecundity experiments. Data from these experiments showed that B. brassicae prefers wild‐type seedlings and M. persicae prefers MINELESS. B. brassicae and M. persicae showed significant variation in establishment on plants regardless of whether they were wild type or MINELESS and also differed significantly in affecting plant parts. Myrosinase activity in MINELESS control seedlings was 83.6% lower than the wild‐type control seedlings. Infestation with either of the two aphid species induced myrosinase levels in both wild‐type and MINELESS seedlings. Infestation with M. persicae reduced the concentration of most glucosinolates while B. brassicae had the opposite effect. B. brassicae enhanced the formation of glucosinolate hydrolysis products both in wild‐type and MINELESS seedlings. However, M. persicae decreased All ITC but increased 3,4ETBut NIT in wild‐type seedlings. Taken together, the investigation shows that the presence of myrosin cells affects the preference of generalist and specialist aphid species for Brassica napus plants.     

Pathogenic Variability within Indian Alternaria brassicae Isolates Using Seed,Cotyledon and Leaf of Brassica Species

Thirty Alternaria brassicae (Berk.) Sacc. isolates from diverse geographical locations of India were studied for pathogenic variability on seed, cotyledon and true leaves of Brassica species. Seed germination was reduced maximum by isolate BAB‐39 in Brassica juncea cultivar Varuna (22.1%), Brassica rapa var. Toria cultivar PT‐303 (12%), Brassica carinata cultivar Kiran (12%), Brassica napus cultivar GSL‐1 (11%) and tolerant source of B. juncea genotype PHR‐2 (7%), although least by isolate BAB‐49. Maximum lesion size on leaf was recorded in B. juncea cultivar Rohini (11.2, 16.5 and 16.8 mm) with isolates BAB‐09 (Pantnagar), BAB‐19 (Bharatpur) and BAB‐39 (Kangra), respectively, and categorized as highly virulent, while minimum lesion size of 3.2, 3.7 and 3.8 mm was observed with isolates BAB‐47 (Tonk), BAB 49 (Jobner) and BAB 04 (Kamroop), respectively, considered the weak isolates. On B. alba, BAB‐09, BAB‐19 and BAB‐39 isolates caused maximum lesion size of 3.7, 3.8 and 3.9 mm, respectively, even though it showed maximum tolerance. In both seed and cotyledon inoculation method, the per cent Alternaria blight severity above 80% was observed with isolate of BAB‐39 (91.5%), BAB‐19 (89.0%), BAB‐09 (85.5%) and least in isolate BAB‐49 (34.0%). Brassica seed, cotyledon and leaf showed the similar positive response for categorizing A. brassicae isolates as virulent and avirulent. This information could be used to the development and assessment of resistant brassica germplasm, especially with A. brassicae populations exhibiting increased virulence.     

Uptake and distribution of sinigrin in microspore derived embryos of Brassica napus L

In Brassica napus, glucosinolates are transported from all parts of the plant into the embryo during seed development. In this study we describe the uptake of the alkenyl glucosinolate sinigrin by microspore derived embryos from high and low glucosinolate genotypes. Microspore derived embryos develop completely isolated from maternal tissues unlike zygotic embryos, which contains glucosinolates transported into the embryo synthesised in the vegetative tissues. The sinigrin in the culture medium was almost completely absorbed by the embryos after three days of culture. The embryos of high and low glucosinolate genotypes were equally capable of absorbing sinigrin from the medium. A significant increase in different alkenyl glucosinolates following feeding of sinigrin suggests induction of biosynthetic enzymes in the embryos. Following excess feeding of sinigrin, we found a strong uptake against a concentration gradient and stable accumulation by the embryos. The glucosinolate was detected in single dissected cotyledons by a photometric test and by HPLC. This test could potentially be useful for screening mutants defective in glucosinolate uptake into the embryo.     

Distinct male reproductive strategies in two closely related oak species

Reproductive strategies of closely related species distributed along successional gradients should differ as a consequence of the trade‐off between competition and colonization abilities. We compared male reproductive strategies of Quercus robur and Q. petraea, two partly interfertile European oak species with different successional status. In the studied even‐aged stand, trees of the late‐successional species (Q. petraea) grew faster and suffered less from intertree competition than trees of the early‐successional species (Q. robur). A large‐scale paternity study and a spatially explicit individual‐based mating model were used to estimate parameters of pollen production and dispersal as well as sexual barriers between species. Male fecundity was found to be dependent both on a tree's circumference and on its environment, particularly so for Q. petraea. Pollen dispersal was greater and more isotropic in Q. robur than in Q. petraea. Premating barriers to hybridization were strong in both species, but more so in Q. petraea than in Q. robur. Hence, predictions based on the competition–colonization trade‐off are well supported, whereas the sexual barriers themselves seem to be shaped by colonization dynamics.     

The Lactoperoxidase System: a Natural Biochemical Biocontrol Agent for Pre‐ and Postharvest Applications

Controlling pests in pre‐ and postharvest crops using natural and low‐impact products is a major challenge. The lactoperoxidase system is an enzymatic system that exists in all external secretions in mammals and is part of the non‐immune system. We tested its efficacy in in vitro microplates on Phytophthora infestans, Penicillium digitatum, Penicillium italicum, Penicillium expansum and Botrytis cinerea to determine the most suitable concentrations for use. Then, we verified its efficacy in planta under controlled conditions. Solutions prepared with 5.4 mm iodide and 1.2 mm thiocyanate and diluted threefold inhibited pathogen growth in vitro by 63–100%. Twofold‐diluted solutions protected potato plants against P. infestans by 60–74% under controlled conditions. Undiluted solution inhibited orange's and apple's postharvest pathogens in curative application with efficacy levels ranging between 84 and 95% in orange and between 63 and 74% in apple. 1.5‐fold concentrated solutions inhibited postharvest pathogens of apple in curative application with efficacy levels ranging between 84 and 92%. Our results also show that the oxidative stress response of fruit following wounding could interfere with ion efficiency. Our tests demonstrate for the first time that this biochemical method is as efficient as a conventional synthetic chemical method under controlled conditions.     

Interactions Between Rhizoctonia Root Rot and the Foliar Common Bean Diseases Anthracnose and Rust

The effects of co‐inoculation of Rhizoctonia solani and Colletotrichum lindemuthianum or Uromyces appendiculatus at different inoculum levels were studied on the disease dynamics and on the growth of bean plants under greenhouse conditions. Bean seeds were sown in R. solani‐infested soil. Additional experiments in which seedlings were transplanted to infested soil were also carried out. Conidial suspensions of C. lindemuthianum or uredospores of U. appendiculatus were inoculated onto leaves at plant developmental stages V2 and V3, respectively. Interactions between root rot and the aerial diseases were observed depending on the inoculum levels and on the timing of R. solani inoculation. Anthracnose severity tended to be higher on R. solani‐infected plants. Conversely, R. solani infection significantly reduced diameter of pustules and rust severity. When seedlings were transplanted to soil infested with low levels of R. solani, root rot severity and density of R. solani in the soil were magnified at high levels of C. lindemuthianum or U. appendiculatus. In these experiments, a synergistic interaction between root rot and anthracnose was observed to affect the plant dry weight. Antagonistic effects on the plant dry weight were found for the combination root rot/rust only when seeds were sown in infested soil.     

First Report of the Occurrence of a White Smut Infecting Rice in Arkansas

False smut has recently emerged as an important disease of rice in Arkansas. In 2011, 2012 and 2013, spore balls of a white smut similar to the spore balls of false smut were observed in rice fields in eastern Arkansas. As a white false smut was previously reported in China and Japan, we examined the morphology of chlamydospores and spore balls from some of the infected heads and used selected regions of the rDNA to determine the identity of the causal agent of the disease. We also tested the virulence of an isolate of the white smut to two rice cultivars commonly grown in Arkansas. Our results indicate that the morphology of the spore balls, chlamydospores and conidia is similar to those reported for Ustilaginoidea albicans. However, sequences of ribosomal DNA amplicons indicate a high degree of similarity with both U. virens and U. albicans. The isolate of the white smut was virulent to two rice cultivars, producing spore balls similar to those observed in the field and to those previously described for U. albicans.     

Control of Colletotrichum coccodes on Tomato by Grafting and Soil Amendments

Eight trials were carried out in 2011 and 2012 in Northern Italy to evaluate the efficacy of grafting, compost and biofumigation with Brassica carinata against Colletotrichum coccodes on tomato. Four trials were carried out in commercial farms, and four trials were carried out in plastic tunnels at an experimental centre. The rootstocks ‘Armstrong’, ‘Arnold’, ‘Beaufort’, ‘Big Power’, ‘Brigeor’, ‘Emperador’, ‘King Kong’, ‘Spirit’ and ‘Superpro V295’ were tested. Host plants included several tomato F1 hybrids: ‘Amantino’, ‘Arawak’, ‘CLX 37438’, ‘Cauralina’, ‘CU 8301’, ‘CU 8506’, ‘DRK 7021’, ‘E 34431’, ‘E 50070’, ‘EXP’, ‘Gotico’, ‘Ingrid’, ‘ISI 61401’, ‘ISI 61402’, ‘Profitto’, ‘Punente’, ‘Rugantino’ and ‘Tomahawk’. Tomato roots from the control plots were 34 to 87% diseased in both naturally and artificially infested soil. Among the nineteen commercial tomato hybrids tested, in the presence of a very high disease pressure in a naturally infested soil, ‘Rugantino’ was the least affected by C. coccodes, showing 32% infected roots. ‘Tomahawk’ grafted onto ‘Arnold’, ‘Armstrong’ and ‘Superpro V295’ was significantly less affected by C. coccodes, while ‘Arawak’ grafted onto ‘Armstrong’, ‘Arnold’, ‘Emperador’ and ‘Beaufort’ provided very good control of root rot in the different trials. Compost addition and biofumigation with Brassica pellets were also tested with and without grafting. Soil amendment with compost, in the case of the ‘Arawak’ and ‘Tomahawk’, resulted in a slightly improved disease control only on non‐grafted plants. When grafting and biofumigation were combined in a soil naturally infested with C. coccodes and Meloidogyne arenaria, biofumigation did not improve C. coccodes control in comparison with grafting alone. In a naturally infested soil, compost alone and combined with biofumigation improved disease control only on non‐grafted ‘Tomahawk’ plants. In general, grafting by itself provided very good results in terms of disease control, which were not significantly improved by combination with compost and/or biofumigation.     

Crotalaria spectabilis and Raphanus sativus as Previous Crops Show Promise for the Control of Bacterial Wilt of Tomato Without Reducing Bacterial Populations

Ralstonia solanacearum is responsible for bacterial wilt affecting many crops worldwide. The emergent population of R. solanacearum (phylotype IIB/4NPB) wilts previously resistant varieties and has rapidly spread throughout Martinique. No conventional method is known to control it. In this study, previous crops used as sanitizing crops were investigated as an environmentally safe alternative method of control. The ability of the emergent population of R. solanacearum to persist in planta and in the rhizosphere of Brassicaceae, Asteraceae and Fabaceae grown as previous crops was evaluated in controlled conditions, and the incidence of bacterial wilt was assessed in the following tomato crop. Results showed that all species carried R. solanacearum latently. Among Brassicaceae and Asteraceae, the highest density of R. solanacearum was found in planta and in the rhizosphere of Tagetes erecta. The density of the R. solanacearum population in the rhizosphere of Raphanus sativus cv. Karacter was significantly higher than that in Raphanus sativus cv. Melody. In Fabaceae, the density of R. solanacearum population in planta was statistically similar in all species. The density of the R. solanacearum population in the rhizosphere of Crotalaria juncea was significantly higher than that in Crotalaria spectabilis. This study showed for the first time that Crotalaria spectabilis and Raphanus sativus cv. Melody grown as previous crops improve the performance of the following tomato with similar effects on R. solanacearum populations in the soil as bare soil. The incidence of the disease in tomato decreased by 86% and 60%, after R. sativus cv. Melody and C. spectabilis, respectively, and the proportion of infected plants also decreased. These results suggest that C. spectabilis and R. sativus cv. Melody can be used as previous crops to help bacterial wilt control in ecological management strategies without drastic suppression of R. solanacearum population in stem tissues and in the rhizosphere.     

Rapid detection of Phytophthora nicotianae by simple DNA extraction and real‐time loop‐mediated isothermal amplification assay

Phytophthora nicotianae is a phytopathogenic oomycete with a wide host range and worldwide distribution. Rapid detection and diagnosis at the early stages of disease development are important for the effective control of P. nicotianae. In this study, we designed a simple and rapid loop‐mediated isothermal amplification (LAMP)‐based detection method for P. nicotianae. We tested three DNA extraction methods and selected the Kaneka Easy DNA Extraction Kit version 2, which is rapid and robust for LAMP‐based detection. The designed primers were tested using mycelial DNA from 35 species (81 isolates) of Phytophthora, 12 species (12 isolates) of Pythium, one isolate of Phytopythium and one isolate each from seven other soil‐borne pathogens. All of the 42 P. nicotianae isolates were detected by these primers, and no other isolates gave positive results. Three isolates were tested for the sensitivity of the reaction, and the lowest amounts of template DNA that could be detected were 10 fg for two isolates and 1 fg for the third. The target was detected within 25 min in all tested samples, including DNA extracted from both inoculated and naturally infected plants. In contrast, PCR assays with P. nicotianae‐specific primers failed or showed weakened detection in several samples. Thus, we found that the rapid DNA extraction and LAMP assay methods developed in this study can be used to detect P. nicotianae with high sensitivity, specificity and stability.     

The ability to manipulate plant glucosinolates and nutrients explains the better performance of Bemisia tabaci Middle East‐Asia Minor 1 than Mediterranean on cabbage plants

The performance of herbivorous insects is greatly affected by host chemical defenses and nutritional quality. Some herbivores have developed the ability to manipulate plant defenses via signaling pathways. It is currently unclear, however, whether a herbivore can benefit by simultaneously reducing plant defenses and enhancing plant nutritional quality. Here, we show that the better performance of the whitefly Bemisia tabaci Middle East‐Asia Minor 1 (MEAM1; formerly the “B” biotype) than Mediterranean (MED; formerly the “Q” biotype) on cabbage is associated with a suppression of glucosinolate (GS) content and an increase in amino acid supply in MEAM1‐infested cabbage compared with MED‐infested cabbage. MEAM1 had higher survival, higher fecundity, higher intrinsic rate of increase (r_m), a longer life span, and a shorter developmental time than MED on cabbage plants. Amino acid content was higher in cabbage infested with MEAM1 than MED. Although infestation by either biotype decreased the levels of total GS, aliphatic GS, glucoiberin, sinigrin, glucobrassicin, and 4OH‐glucobrassicin, and the expression of related genes in cabbage, MED infestation increased the levels of 4ME‐glucobrassicin, neoglucobrassicin, progoitrin, and glucoraphanin. The GS content and expression of GS‐related genes were higher in cabbage infested with MED than with MEAM1. Our results suggest that MEAM1 performs better than MED on cabbage by manipulating host defenses and nutritional quality.     

Phylogeny and assemblage composition of Frankia in Alnus tenuifolia nodules across a primary successional sere in interior Alaska

In nitrogen (N) fixing symbioses, host‐symbiont specificity, genetic variation in bacterial symbionts and environmental variation represent fundamental constraints on the ecology, evolution and practical uses of these interactions, but detailed information is lacking for many naturally occurring N‐fixers. This study examined phylogenetic host specificity of Frankia in field‐collected nodules of two Alnus species (A. tenuifolia and A. viridis) in interior Alaska and, for A. tenuifolia, distribution, diversity, spatial autocorrelation and correlation with specific soil factors of Frankia genotypes in nodules collected from replicated habitats representing endpoints of a primary sere. Frankia genotypes most commonly associated with each host belonged to different clades within the Alnus‐infective Frankia clade, and for A. tenuifolia, were divergent from previously described Frankia. A. tenuifolia nodules from early and late succession habitats harboured distinct Frankia assemblages. In early succession, a single genotype inhabited 71% of nodules with no discernable autocorrelation at any scale, while late succession Frankia were more diverse, differed widely among plants within a site and were significantly autocorrelated within and among plants. Early succession Frankia genotype occurrence was strongly correlated with carbon/nitrogen ratio in the mineral soil fraction, while in late succession, the most common genotypes were correlated with different soil variables. Our results suggest that phylogenetic specificity is a significant factor in the A. tenuifolia‐Frankia interaction and that significant habitat‐based differentiation may exist among A. tenuifolia‐infective genotypes. This is consistent with our hypothesis that A. tenuifolia selects specific Frankia genotypes from early succession soils and that this choice is attenuated in late succession.