Kazuto Iwama

Stable Characteristics of Cover Crops for Weed Suppression in Organic Farming Systems

Abstract:The use of cover crops is an effective technique to control weeds, which are one of the most serious problems for crop production without using herbicides. This study investigated the characteristics of cover crops for weed suppression at an organic farming field in a snowy-cold region, Hokkaido. Nine, three and two species of cover crops comprising both Poaceae and Leguminosae were grown in 2003, 2004 and 2005, respectively, at different sowing densities from 50 to approximately 4000 seeds m-2. The relationships between weed dry matter production and characteristics of cover crops, such as plant height and coverage, were investigated at 4 and 10 weeks after cover crop sowing (WAS). Correlation analysis of the weed dry weight with characteristics of cover crops revealed that the cover crop coverage at 4 WAS had a strong and stable effect on weed suppression. The cover crop coverage at 4 WAS was affected primarily by their seed weight when cover crops with a large variation in seed weight were used, and by the sowing density when cover crops with a small variation in seed weight were used. These results suggest that to achieve high weed suppression it is important to obtain higher coverage at the early growth stage of the cover crops with a heavy seed weight and high sowing density.

Effect of cultivar maturity period on the growth and yield of potato plants grown from microtubers and conventional seed tubers

Potato plants of early cultivars grown from microtubers have been reported to have a much lower growth vigor and produce lower yields than microtubers of late cultivars. This study intended to clarify the field performance of plants grown from directly planted microtubers of cultivars with different maturity periods, with a special attention to early cultivars. The experiments were conducted at Hokkaido University, Japan, over four years. Microtubers and conventional seed tubers of the early cultivar Kitaakari, late cultivars Konafubuki and Norin 1, and very late breeding line IWA-1 were planted, and the plant growth and tuber yields were analyzed. The microtuber plants of Kitaakari had a lower initial increase in leaf area index than conventional seed tuber plants, but at the maximum shoot growth had the same leaf area index. This pattern was also observed in the other cultivars. Tuber initiation and tuber bulking occurred on average five days later in microtuber plants than in conventional seed tuber plants of cultivar Kitaakari. At maximum shoot growth, microtuber plants had on average 65% of tuber dry weight of conventional seed tuber plants, with small variation among cultivars. Irrespective of maturity period, microtuber plants showed a higher tuber increase after maximum shoot growth, achieving around 86% of tuber dry weight of conventional seed tuber plants at harvest. From the results of this study we conclude that microtuber plants of early and late cultivars have a similar yield potential relative to conventional seed tuber plants, and microtubers of both early and late cultivars might be used as an alternative seed tuber source for potato production, if necessary.ResumenSe ha reportado que las plantas precoces de papa, provenientes de microtubérculos tienen mucho menos vigor y menor rendimiento que las de cultivares tardios derivados de microtubérculos. Este estudio tiene la intención de esclarecer el comportamiento en campo de plantas de cultivares con diferente período de madurez que provienen directamente de microtubérculos, con especial atención a los cultivares precoces. Los experimentos se realizaron en la Universidad de Hokaido, Japon durante cuatro años. Se plantaron microtubérculos y tubérculos-semilla convencionales del cultivar Kitaakari, de cultivares tardíos de Konafubuki y Norin 1, y de la línea de mejoramiento muy tardía IWA-1 y se analizó el desarrollo de las plantas y los rendimientos. Las plantas derivadas de microtubérculos de Kitaakari tuvieron un menor índice de crecimiento del área foliar que las plantas originadas de tubérculos-semilla, pero cuando los brotes alcanzaron el crecimiento máximo, mostraron igual índice de área foliar. Este patrón fue también observado en los otros cultivares. El inicio de la tuberización y aumento del volumen del tubérculo de plantas provenientes de microtubérculos se produjo cinco dias después que en las plantas derivadas de tubérculos-semilla del cultivar Kitaakari. Al momento del máximo crecimiento de los brotes, las plantas provenientes de microtubérculos tenían en promedio el 65% del peso seco de las plantas originadas de tubérculossemilla con una ligera variación entre cultivares. Prescindiendo del período de madurez, las plantas originadas de microtubérculos mostraron un mayor incremento del tubérculo después del máximo crecimiento de los brotes, alcanzando a la cosecha alrededor del 86% del peso seco del tubérculo de las plantas provenientes de semilla convencional. Tomando como base los resultados de este estudio, concluimos que las plantas provenientes de microtubérculos de cultivares precoces tienen potencialmente un rendimiento similar en relación con las plantas provenientes de tubérculossemilla convencionales y los microtubérculos tanto de cultivares precoces como tardíos pueden ser usados en caso necesario como fuente alternativa de semilla para la producción de papa.

Growth and yield of potato plants grown from microtubers in fields

Despite many reports of thein vitro production of microtubers, little is known about plant growth and yield from microtubers planted in the field. This study clarified differences in growth and yields between potato plants grown in the field from microtubers and from conventional seed tubers. The experiments were performed at Hokkaido University, Japan, over four years. Conventional seed tubers of about 50 g and microtubers of two sizes (0.5–1.0 g and 1.0–3.0 g) of the latematurity cultivar Norin 1 were planted, and plant growth and tuber yields were analyzed. The microtuber plants had a lower initial increase in root and leaf area index than conventional seed tuber plants, but had the same leaf area index after about 40 days from emergence. The first tuber formation in microtuber plants was about 7 days later than in conventional seed tuber plants, while tuber bulking occurred about 14 days later in microtuber plants. Consequently, the onset of tuber weight increase was later in microtuber plants, but the rate of increase thereafter was similar between conventional seed tuber and microtuber plants. At harvest the tuber fresh weight of microtuber plants was 82% that of conventional tuber plants, suggesting a potential for using microtubers for field planting.ResumenA pesar de los muchos reportes sobre producción de microtubérculosin vitro, se conoce muy poco acerca del desarrollo y rendimiento de las plantas provenientes de microtubérculos en el campo. Este estudio pone en claro las diferencias en desarrollo y producción en el campo de plantas provenientes de microtubérculos con las provenientes de tubérculo semilla convencional. Los experimentos se realizaron en la Universidad de Hokkaido, Japón durante cuatro años. Se sembraron tubérculos de semilla convencional de unos 50 g y microtubérculos de dos tamaños (0.5 a 1.0 g y 1.0 a 3.0 g) del cultivar de maduración tardía Norin 1, y se analizó tanto el desarrollo de las plantas como el rendimiento de los tubérculos. Las plantas provenientes de microtubérculos mostraron un incremento inicial del índice en área de raíces y hojas menor que las plantas provenientes de tubérculo semilla convencional, pero 40 días después de la emergencia, el índice de área foliar fue la misma. Las plantas de tubérculo semilla convencional y las plantas de microtubérculos mostraron muy poca diferencia en cuanto al numéro de días en que se produjo el inicio de la formación de tubérculos, pero el aumento en el volumen del tubérculo se produjo 10 dias después, en las plantas provenientes de microtubérculos. El incremento en tubérculos y peso seco total desde el comienzo de la formación de tubérculos hasta el maximo crecimiento de los vástagos fue mayor en las plantas originadas de tubérculo semilla convencional que en las plantas provenientes de microtubérculos. Al momento de la cosecha, el peso fresco de tubérculos de plantas provenientes de microtubérculos fue 82% de aquel proveniente de plantas de tubérculos convencionales, lo cual sugiere que los microtubérculos tienen potencial para su uso en el campo.

Effects of Planting Date on the Growth and Yield of Two Potato Cultivars Grown from Microtubers and Conventional Seed Tubers

Abstract This study clarified the effect of planting date on the growth and yield of potato (Solanum tuberosum L.) plants grown from conventional seed tubers (CT) and microtubers (MT). CT of about 50 g and MT of 1 to 3 g of early (Kitaakari) and late (Norin 1) maturity cultivars were planted at Hokkaido University, Sapporo, Japan, on May 13, June 4 and June 25, and their growth and yields were investigated. The linear increase in leaf area index started later, but thereafter was higher in MT plants than in CT plants, irrespective of cultivar and planting date. Tuber formation was later in MT plants than in CT plants of both cultivars, but this difference was smaller on the last planting date. The linear increase in tuber dry weight started later in MT plants than in CT plants, but the rate of increase was similar in MT and CT plants of both cultivars and on all planting dates. Delaying the date of planting reduced the tuber yield, mainly because of the shortening growing period in MT and CT plants. The reduction in tuber yield and growing period was greater for the late cultivar Norin 1 compared with the early cultivar Kitaakari of CT and MT plants. Despite the climatic variations among the planting dates, MT plants yielded 71 to 90% of tuber fresh weight relative to CT plants, suggesting that MT are a good alternative as propagules for potato cultivation in countries where seed production is difficult.

Genotypic Variation of the Ability of Root to Penetrate Hard Soil Layers among Japanese Wheat Cultivars

Abstract The hard soil in the field is a major constraint for the cereal production because it mechanically restricts the root expansion and water absorption. The ability of root to penetrate into the hard soil is an important factor affecting yield stability of wheat (Triticum aestivum L.) under hard soil and drought conditions. We investigated the variation in the penetrating ability of roots (PA) among Japanese wheat cultivars and its relationship with other shoot and root characters to acquire basic information to develop the cultivars with a higher PA. The evaluation was conducted by the two experiments using the two groups of cultivars: 1) 43 Hokkaido cultivars in the first experiment, 2) 38 Honsyu, including Shikoku and Kyusyu, cultivars in the second experiment. In each experiment, one seedling of each cultivar was grown in a pot with a disc made of paraffin and Vaseline mixture (PV) as a substitute for the hard soil layer. The number of roots penetrating through the PV disc per plant (NRP), the number of seminal and crown roots reached the PV disc per plant (NRR) and the penetration index (PI = NRP/NRR) of each cultivar were evaluated as the traits related to PA. NRP significantly varied with the cultivar from 4.0 to 29.7 and 3.0 to 22.0 in the first and second experiments, respectively. NRP were significantly correlated with NRR (r=0.644** in the first and r=0.477** in the second experiment) and PI (r=0.863** in the first and r=0.811** in the second experiment), but the relationships between NRR and PI were not significant (r=0.260 in the first and r=0.190 in the second experiment). NRR was significantly correlated with the degree of winter growth habit (requirement of vernalization), root dry weight (DW) above the PV disc, the number of stems and leaf DW in each population. Correlations between PI and other characters were low or not significant. These results indicate that a large genotypic variation exists among Japanese wheat cultivars in NRP, and that PI is a suitable indicator of PA. Cultivars with a high PA detected in this study will be useful genetic resources of wheat to improve the yield stability under drought and hard soil conditions.

Relationship between Deep Root Distribution and Root Penetration Capacity Estimated by Pot Experiments with a Paraffin and Vaseline Layer for Landraces and Recent Cultivars of Wheat

Root growth into deep soil is an important factor for stable production in wheat under drought conditions. Root penetrating capacity (RP) shown by pot experiments with a paraffin-Vaseline layer (PV layer) may be a useful indicator estimating deep rooting ability of wheat genotypes. Previously, we identified genotypes of durum wheat (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) with diverse RP by the pot experiments. In this study, we investigated the root distribution of three Ethiopian landraces of durum wheat with high RP, three recent cultivars of durum wheat with low RP and one Japanese cultivar of bread wheat ‘Haruyutaka’ with low RP using: (1) pots with a PV layer, (2) root boxes, (3) artificial field and (4) a normal field to analyze the relationship between RP estimated by pot experiment and root development in the field. In the pot experiments, RP was evaluated by the number of roots penetrating through the PV layer (NRP). In the root-box and field experiments, the root distribution was evaluated by the number of roots on the vertical surface of soil as the root frequency (RF: root number cm-1 soil surface). Ethiopian landraces had a significantly larger NRP than recent cultivars in the pot experiment. The root box and field experiments showed that Ethiopian landraces tended to have a higher RF than recent cultivars in deep soil layer. We concluded that RP estimated by pot experiments with a PV layer is a useful indicator of deep rooting ability under field conditions.

The reduced height genes do not affect the root penetration ability in wheat

Root penetration (RP) ability into compacted soil is an important breeding target for drought avoidance by durum (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) in regions with compacted soils and water deficits. However, it is said generally that yield of the current cultivars introduced the reduced height gene (Rht-B1b or Rht-D1b) are more sensitive to drought stress than that of old landraces. This study investigated the effect of the Rht genes on RP ability using the seedlings of near-isogenic lines (NILs) of Rht genes of ‘LD222’ durum wheat and ‘April Bearded’ bread wheat, and 110 recombinant inbred lines (RILs) of durum wheat derived from the cross between the tall landrace (Jennah Khetifa; Rht-B1a Rht-B1a) and semi-dwarf cultivar (Cham1; Rht-B1b Rht-B1b). One seedling of each genotype was grown in a pot (6 cm diameter, 15 cm height) with a disc of 3 mm thickness made from paraffin and Vaseline mixture (PV) in 10 cm depth, as a substitute for a compacted soil layer. The RP index [number of roots penetrating through the PV disc per plant (PVRN)/total number of seminal and crown roots per plant (TRN)] was measured at eight weeks after sowing and used as the indicator of RP ability of seedling. In NILs, the shoot length decreased significantly because of the introduction of either Rht-B1b or Rht-D1b dwarfing genes, but the RP index was similar to those of tall parents. In RILs, although the RP index and shoot length were higher in Jennah Khetifa than in Cham1, the relationship between RP index and shoot length was not significant (r = 0.156). Both results indicate that RP ability of wheat does not link to dwarfness regulated by Rht genes. We suppose therefore that it would be possible to develop a high yielding semi-dwarf cultivar with excellent RP ability.

Endogenous Components and Tissue Cell Morphological Traits of Fresh Potato Tubers Affect the Flavor of Steamed Tubers

Fresh potato tubers of 13 different cultivars were analyzed for endogenous components and morphological traits in intact cells to study the relationship between traits of fresh tubers and the flavor of cooked (steamed) potato. Deliciousness composed of sweetness, potato taste and smoothness was significantly different between the cultivars; the tasting evaluations were reasonable when considering each tuber utilization, i.e. deliciousness of vegetable potato tended to be higher than that of the others, potato for processing and starch. The three main tasting traits were each related significantly, particularly potato taste had strong-negative correlation with sweetness and smoothness of tuber. The main tasting traits also had strong relationships to the starch content in cortex tissue of potato tubers. The starch content was significantly related negatively to potassium, phosphorus and cell size of cortex and they were related positively to smoothness of steamed tuber. The sweetness of steamed tuber was related negatively to the starch content, and the pH of the extract solution from cortex tissue was related significantly to both traits, sweetness and starch content. The potato taste of steamed tubers was related positively to starch content, but sweetness was significantly related negatively to potato taste by the physical traits of cortex tissue, pulp hardness and strength of cell wall binding. Thus, complicated flavor-linkages pivoting on starch through endogenous component and pH seemed to influence the deliciousness of steamed tubers, but traits that had no relation with starch content were also detected, such as silicon content. These results of this study may be useful for breeding potato cultivars with Japanese desirable flavor traits for use as vegetables.ResumenTubérculos frescos de papa de 13 cultivares diferentes fueron analizados en relación a sus componentes endógenos y características morfológicas en células intactas para estudiar la relación entre las características de tubérculos frescos y el sabor de papas cocinadas al vapor. Su exquisitez compuesta por dulzura, sabor a papa, y suavidad fueron significativamente diferentes entre cultivares; las evaluaciones de sabor fueron razonables cuando se consideraban el uso de cada tubérculo; i.e., la exquisitez de la papa vegetal tiende a ser mayor que otras, por ejemplo, papas para procesamiento y almidón. Las tres principales características de sabor se relacionaban significativas, particularmente el sabor de la papa tuvo una fuerte correlación negativa con la dulzura y el sabor del tubérculo. Las principales características de sabor estuvieron fuertemente relacionadas con el contenido de almidón en la corteza de los tubérculos. El contenido de almidón fue relacionado significativamente en forma negativa con el potasio, fósforo y tamaño de la célula de la corteza, y fueron relacionados positivamente con la suavidad del tubérculo cocido al vapor. El sabor dulce de la papa cocida al valor fue negativamente relacionada con el contenido de almidón; y el pH de la solución extraída del tejido de la corteza se relacionó fuertemente con ambas características de dulzura y contenido de almidón. El sabor de las papas al vapor fueron positivamente relacionadas al contenido de almidón, pero su sabor dulce fue negativamente relacionado al sabor de la papa por las características físicas de su corteza, dureza de la pulpa, y la fuerza en la obstrucción de la pared celular. Así, el complicado acoplamiento de sabor que gira en torno al almidón a través de los componentes endógenos y el pH, parecen influenciar en la exquisitez de las papas al vapor; pero algunas características que no tienen ninguna relación con el contenido de almidón, como el silicio, también fueron detectados. Los resultados de este estudio podrían ser útiles en el mejoramiento de cultivares de papas con características de sabor deseables para los japoneses para su uso como vegetales.

Interseeding a Cover Crop as a Weed Management Tool is More Compatible with Soybean than with Maize in Organic Farming Systems

Abstract Weeds are the most serious threat to crop production in organic farming systems. Information on the spatial distribution of weeds is important for effective weed management. The objective of this study was to evaluate the effect of the ground cover of the main crops (soybean and maize) and cover crop on the spatial distribution of weeds for two row sections, ‘within the row (IR)’ and ‘between the rows (BR)’. The cover crop was interseeded in BR 3 – 4 weeks after sowing the main crops in two years, and weed density and vegetation cover ratio (VCR, an index of ground cover) of the main crops and cover crop were measured. There was a significant difference in the spatial distribution of weeds between the two main crops. In IR, weed density was higher in maize than in soybean, while in BR, it was higher in soybean. This means that weed suppression in IR was more important for maize, while the suppression in BR was more important for soybean. The negative relationship between VCR of the main crop plus cover crop and weed density in each row section suggests that the difference in ground cover was one of the reasons for the difference in weed density between the two main crops. The cover crop markedly increased the VCR in BR, but only slightly increased VCR in IR in both main crops. These results suggest that the cover crop was more compatible with soybean than with maize, because the high weed density in IR of maize could not be decreased sufficiently by the slight increase of VCR in BR by the cover crop.

Effect of Potato Microtuber Size on the Growth and Yield Performance of Field Grown Plants

Abstract To examine the effect of the size of the potato microtuber (MT) produced in vitro on the posterior field performance, we examined the growth and yield of the late maturity cultivar Norin 1 using four sizes of MT: 0.3–0.5 g, 0.5–1 g, 1–3 g and 3–5 g, and conventional seed tubers (CT) (approximately 50 g). The experiment was conducted at Hokkaido University, Sapporo Japan in 1998 and 1999. The tubers were planted in May of each year, in a randomized block design with three replications. Plants from MT lighter than 0.5 g showed a slower initial leaf and tuber growth than heavier MT, but around the full flowering stage there was no significant difference with the MT size in leaf or tuber growth. CT plants showed higher initial leaf and tuber growth compared with MT plants, especially in 1999. No differences in growing period, number of tubers, and tuber fresh and dry yield were observed with the MT size. However, in 1999, the growing period was longer and tuber fresh and dry yields at harvest were higher in CT plants. MT of all sizes used in the study can be used for direct field planting, but more studies are needed to increase the yield stability of MT plants.