We plotted the highlighted spectral bands into Fig. 3, and it is seen that the selected spectral bands in each LDA-based classification were located near known pigment peaks involved in photosynthesis and/or near spectral bands used in published indices to predict chlorophyll or nitrogen content in leaves. Thus, it appears that seed germination may be successfully classified based on reflectance in narrow spectral bands associated with the primary metabolism function and performance of plants. Although this study has demonstrated proof of concept in the potential utilization of machine-vision systems for managing ex situ seed resources several questions remain. Seeds in this study were aged under artificial conditions so the seed coat changes detected using hyperspectral analysis may not be indicative of changes that occur to seeds when stored under standard seed bank conditions. Across the plant kingdom, seeds vary greatly in colors, color patterns, shapes, and sizes. In addition, they have species-specific responses to environmental conditions. Different classification algorithms were therefore used for each of the three seed species, and successful use of this technology among other native plant species will require development of species specific classification algorithms. Availability of machine-vision systems to automate non-destructive assessments of seed germination may greatly improve the management of seed banks in future once further more detailed assessments of the technology are undertaken. Indeed, it may also be possible that such machine-vision systems can be used in advanced research into seed dormancy and other studies of seeds and their responses to environmental conditions and thus provide fresh insights into the underlying seed biology and physiology.
California organic strawberry producers face the challenge of controlling soil borne diseases,ebb and flow bench notably Verticillium wilt caused by Verticillium dahliae, Fusarium wilt caused by Fusarium oxysporum and charcoal rot caused by Macrophomina phaseolina . The main approach used to control these pathogens is crop rotation, however, many of the vegetable crops that can economically be rotated with strawberry are also hosts to one or more of the pathogens. Brassica species, notably broccoli have been found to suppress V. dahliae , but other key crops like lettuce are hosts. Furthermore, microsclerotia of V. dahliae can persist in the soil for many years. There is a clear need for additional disease control strategies and two that have shown promise are anaerobic soil disinfestation and use of mustard seed meals . Anaerobic soil disinfestation was developed in Japan and The Netherlands and has been shown to control soilborne pathogens and nematodes in strawberries. Previous studies conducted were aimed at optimizing ASD for California strawberry systems, and in conventional systems ASD was shown to be consistently effective at suppressing Verticillium dahliae in coastal California when 20 t ha-1 of rice bran was pre-plant incorporated and 75 to 100 mm of irrigation was applied in sandy-loam to clay-loam soils . California berry growers have started to adopt ASD at a commercial scale with ASD acreage increasing from 2 ha to over 400 ha in the last four years , the majority in organic production.It has also been evaluated in strawberry systems and showed neutral to positive effects on fruit production and disease suppression when used alone or in combination with other non-fumigant approaches such as ASD. Here we report on a recent rotation experiment testing ASD and MSM in a long term organic field site, and some large scale field demonstrations carried out in two different regions of California.In June 2011, a 4 replicate randomized block split-plot experiment with crop rotation as the main plots and ASD, mustard seed meal , ASD+ MSM, and untreated control as sub plots was established at the Center for Agroecology and Sustainable Food Systems organic farm on the University of California, Santa Cruz campus.
After strawberries, a legume/cereal mix winter cover crop was planted and followed with summer lettuce in all treatment plots. For management details see Zavatta et al. . Briefly broccoli ‘Gypsy’ and cauliflower ‘Snow crown’ were grown from June to September 2011 as main plots which were split prior to planting strawberries. For ASD plots, 20 t ha-1 of rice bran was applied to the bed surface and rototilled to 15 cm depth. For MSM plots 3.4 t ha-1 MSM was incorporated. For ASD+MSM plots, 16.9 t ha-1 of rice bran and 3.4 t ha-1 of MS were applied. ASD and ASD+MSM plots were drip irrigated to create and sustain anaerobic conditions for 3 weeks with a total of 108 mm of water applied. Strawberry plants ‘Albion’ were transplanted in November 2011, and fruit yield monitored from 20 plants bi-weekly from April to September 2012. A legume/cereal cover crop , 45% vetch , 10% rye was planted in all plots in the fall 2012 and grown until the following spring at which time they were mowed and incorporated into the soil. Romaine lettuce ‘Salvius’ was grown in the summer 2013. The numbers of viable V. dahliae microsclerotia in 0-15 cm of soil were estimated using a modified Anderson sampler and NP10 selective medium before and after each crop, and pre- and post-ASD treatment. V. dahliae infection on strawberry plants was evaluated at the end of the growing season for four plants per plot. A split plot ANOVA was used for statistical analysis. Two non-replicated large-scale ASD demonstration trials were conducted at a grower’s farm in Watsonville, California during the 2012-2013 growing season. One trial was on conventionally farmed land and the other in a nearby organic field. Main treatments were ASD using rice bran at 20 t ha-1 or RB 10 t ha-1 + Molasses 10 t ha-1, and subtreatments with or without pre-plant fertilizer. For the conventional field, a 673 kg ha-1 of slow release fertilizer was added pre-plant, and for the organic site feather meal at a rate of 1,122 kg ha-1. For ASD, RB 20 or 10 t ha-1 was broadcast onto the assigned plots and rototilled to a depth of 15 cm. Beds were formed, drip tapes and plastic mulch applied, and the first irrigation began two days later. Mol was diluted with water at 1:2 to 1:5 in a water tank prior to application, then 6.5 t ha-1 was applied through the drip tapes. Seven days later,hydroponic growing the remaining Mol was applied in the same manner. All plots were intermittently drip irrigated for three weeks from the first irrigation, with total irrigation amount of 60-75 mm. Soil Eh at 15 cm depth was monitored continuously using ORP sensors connected to a datalogger. Strawberries were harvested from 4 sections of each plot bi-weekly from March 19 to October 28, 2013.
A second strawberry demonstration trial was established in Oxnard, CA, in August 2014 with unreplicated 0.4 ha blocks of treatments of ASD RB 20 t ha-1, ASD RB 15 t ha-1, MSM 5.6 t ha-1 and grower standard practices. A 2.24 t ha-1 of pre-plant organic fertilizer was applied only to the grower standard plot. The same treatments, except for the RB 15 t ha-1 plot, had been applied to the same plots for the previous strawberry crop which was followed by a wheat cover crop incorporated in early August 2014. Instead of RB 15 t ha-1, the previous treatment had been ASD using RB 6.7 t ha-1 plus MSM 4.5 t ha-1 as Csources. RB and MSM were both applied on August 25 by broadcaster then beds shaped, drip lines added and TIF plastic tarp laid down. Approximately 200 mm of water was applied during ASD. Anaerobic conditions and soil temperatures were measured during ASD as above, and strawberries were harvested by the grower from January to May 2015. Plant mortality was measured by counting dead or nearly dead plants in each plot. Soil samples were taken from 0 to 6 inch depth in all plots post-treatment for microbial analysis by USDA-ARS WA using real-time quantitative PCR and terminal restriction fragment length polymorphism analysis. There was no significant effect of previous crop on the growth and yield response of strawberries irrespective of the disease management strategy used . However, when averaged across all previous crop treatments yields were highest in the ASD treatment with RB+MSM as the carbon source and ASD with RB only . This was likely due to a combination of enhanced fertility in the early season and disease suppression in the later season. Indeed disease severity was significantly reduced with the ASD treatments . What is particularly inTheresting, however, is that the numbers of V. dahliae microsclerotia present in the soil were still lower in the ASD treatments almost 2 years later . This is despite a cover crop being grown and incorporated and a lettuce crop produced in the interim, and suggests a long term suppression of disease by the ASD treatment. This agrees with observations by Goud et al. that ASD provided long term suppression of V. dahliae, but in their case the soil was undisturbed during the intervening 3 years. As discussed below, microbial community changes associated with ASD have been found to persist for many months and may be responsible for the longer term suppression. Excellent anaerobic conditions were created in this field demonstration , in both the organic and conventional fields and were associated with excellent strawberry yields . Previous work found that around 50,000 mV h below 200 mV was necessary for good control of V. dahliaand this threshold was greatly exceeded in both fields. In the conventional fields yields were equivalent to the adjacent fumigated areas, and in both cases there was little or no additional yield benefit from adding pre-plant fertilizer. Rice bran and MSM both contain large amounts of nutrients which can substitute for preplant fertilizer, however, current work is focusing on either reduced rates of application or alternative carbon sources to avoid potential excess losses of nutrients into the environment. Treatments connected by a line are not significantly different at p<0.05 . Main plot treatments are previous crop: fallow, broccoli or cauliflower; and sub plots: ASD=ASD 20 t ha-1 rice bran, ASD+MC=ASD 16.9 t ha-1 rice bran + 3.4 t ha-1 mustard seed meal, MC=3.4 t ha-1 mustard seed meal, UTC = untreated control. Macrophomina phaseolina is present at this location and is a serious concern for strawberry production. In both years of the demonstration ASD greatly improved crops yields relative to the grower’s standard practice and reduced disease severity as measured by crop mortality . The second year trial again demonstrated that no pre-plant fertilizer was necessary at ASD RB 20 t ha-1 plot. There was a significant shift in fungal community composition in soils post ASD, relative to the MSM and the grower standard . However, prior to treatment the following year and after an intervening wheat cover crop, the ASD RB9 treatment still clus.
Thered together and were distinct from the other plots again indicating longer term changes in the soil following ASD. Following the second year with ASD treatment soil fungal communities again showed very distinct clustering based on treatment . This pattern has been observed in other field trials and we are in the process of identifying which species become more prevalent following ASD and if this is related to type of carbon source. Initial screening of NextGen sequencing data suggest that enhanced strawberry yields in response to ASD conducted using rice bran was associated with elevated detection of sequences representing various genera within the Flavobacteria known to have anti-fungal properties. In this opinion-based article, we discuss how indirect effects of drought may adversely affect both the performance of systemic insecticides and also lead to increased risk of insect pests developing behavioral insecticide resistance. Furthermore, we argue that the possible adverse effects of drought on the performance of systemic insecticides has to be given increased research attention, as climate change will likely lead to increased severity and frequency of drought in many agricultural regions. The Food and Agriculture Organization of the United Nations defines a pesticide as “Any substance or mixture of substances intended for preventing, destroying, or controlling any pest … The term includes substances intended for use as a plant growth regulator, defoliant, desiccant, or agent for thinning fruit or preventing the premature fall of fruit.” . Systemic insecticides are chemicals absorbed by plants and distributed internally via the vascular system, delivering the insecticide to untreated plant tissues .