DOI: 10.5061/dryad.69p8cz92t
title: Context-dependent effects of Trichoderma seed inoculation on anthracnose disease and seed yield of bean (Phaseolus vulgaris): ambient conditions override cultivar-specific differences

description: Root colonizing Trichoderma fungi can stimulate plant immunity, but net
 effects are strain × cultivar-specific and changing ambient conditions
 further contribute to variable outcomes. Here, we used four Trichoderma
 spp. to inoculate seeds of four common bean (Phaseolus vulgaris) cultivars
 and explored in three different experimental setups the effects on fungal
 anthracnose after leaf inoculation with Colletotrichum lindemuthianum.
 Plants growing in pots with field soil under greenhouse conditions
 exhibited the highest and those in the open field the lowest overall
 levels of disease. Among 48 Trichoderma strain × bean cultivar × setup
 combinations, Trichoderma-inoculation enhanced disease in six and
 decreased disease in ten cases, but with the exception of T. asperellum
 B6-inoculated Negro San Luis beans, the strain × cultivar-specific effects
 on anthracnose severity differed among the setups, and anthracnose
 severity did not predict seed yield in the open field. In the case of Flor
 de Mayo beans, Trichoderma even reduced yield in anthracnose-free field
 plots, although this effect was counterbalanced in anthracnose-infected
 plots. We consider our work as a case study that calls for stronger
 emphasis on field experiments in the early phases of screenings of
 Trichoderma inoculants as plant biostimulants.
description: The seeds of the four
 common bean cultivars Flor de Junio Marcela (FJM), Flor de Mayo Anita
 (FMA), Pinto Villa (PV) and Negro San Luis (NSL) were inoculated each of
 with the <i>Trichoderma</i> strains  <i>T.
 longibrachiatum</i> MK1, <i>T. asperellum</i> B6,
 <i>T. atroviride</i> P1 and <i>T. harzianum</i> T2
 (or no <i>Trichoderma</i> as control) and cultivated in three
 different experimental setups: (A) in pots with a sterile, commercial
 substrate in a greenhouse, (B) in pots with non-sterile field soil in the
 greenhouse and (C) in open field plots. The field experiment was performed
 in the experimental field of CINVESTAV Unidad Irapuato (State of
 Guanajuato, 1.800 m above sea level: 20°43′13″ N; 101°19′43″ W) during the
 spring-summer season of 2019 (from March to August). We established four
 subplots, two subplots assigned to inoculation with
 Colletotrichum, the other two subplots as anthracnose-free controls. On 26 and 27<sup> </sup>March, <i>n</i> = 8 seeds per strain × cultivar combination and subplot were sown directly into the soil in a completely randomized spatial distribution. In all three setups, plantlets with 3–5 trifoliate leaves were leaf-challenged with <i>Colletotrichum lindemuthianum. </i>The severity of anthracnose disease was quantified 20 days after the challenge with <i>C. lindemuthianum</i>, collecting one randomly selected leaf per plant which was scanned using a printer equipped with scanning function (Brother DCP-1602) to subsequently determine the total leaf area and the diseased leaf area using the image analysis software Image J and to calculate the percentage of affected area for each leaf. In case of the field—grown plants, in addition to quantifying the diseased area, the area removed or visibly damaged by herbivores was quantified to calculate herbivore damage as percentage of the total area. Subsequently, plants were allowed to finish their growing cycle. At the end of the reproductive phase, i.e., when plants started to dry naturally, we first counted the number of plants that had survived until reproduction. Plants were harvested individually (either all plants or in case of survival of more than five plants per subplot, a maximum of five randomly selected plants per strain ×x cultivar combination and subplot), the pods were removed and opened manually and the seeds dried in an oven at 50 °C for two days, to determine seed dry weight per plant.