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Surface texturing is a widely accepted approach for friction reduction between mechanical components. Through-mask electrochemical micromachining is a simple and reliable process for metal surface texturing in which mass transport conditions have profound influence on final machined quality. An ultrasonic stirrer is usually adopted for mass transfer enhancement. However, understanding of the effects of ultrasonic stirring on mass transfer is limited, and is far from sufficient for developing guidelines for its practical application. In this work, the influences of ultrasonic stirring parameters on mass transfer have been investigated numerically and experimentally. With the numerical method, periodic pressure change in the electrolyte over time has been obtained, showing that ultrasonic stirring results in drastic transient pressure change in electrolyte fluid fields. Parameters related to ultrasonic frequency, vibration amplitude, and the depth of anode surface immersed in the electrolyte solution influence pressure amplitude. Validation experiments have been conducted and etched surface profile and morphology characterized, which show that the experimental observations are in agreement with numerical predictions. With the optimized mass transfer, well-defined micro-pits array of 30 μm and a smooth etched surface on tin-bronze substrate in large scale have been demonstrated.

We found gene introgression from cultivated rice to its in situ conserved wild relative populations, which has considerably altered their genetic structure and relationship. The level of introgression is associated with the spatial distances of the wild populations from cultivated rice fields. The findings are based on genetic analyses of six wild populations and two sets of rice cultivars using two types of molecular markers. Crop-wild introgression alters the genetic integrity of wild populations. Thus, appropriate measures should be taken for effective in situ conservation of wild relatives of crop cultivars., Maintaining genetic integrity is essential for in situ and ex situ conservation of crop wild relative (CWR) species. However, introgression of crop alleles into CWR species/populations may change their genetic structure and diversity, resulting in more invasive weeds or, in contrast, the extinction of endangered populations. To determine crop-wild introgression and its consequences, we examined the genetic structure and diversity of six wild rice (Oryza rufipogon) populations under in situ conservation in China. Thirty-four simple sequence repeat (SSR) and 34 insertion/deletion markers were used to genotype the wild rice populations and two sets of rice cultivars (O. sativa), corresponding to the two types of molecular markers. Shared alleles and STRUCTURE analyses suggested a variable level of crop-wild introgression and admixture. Principal coordinates and cluster analyses indicated differentiation of wild rice populations, which was associated with the spatial distances to cultivated rice fields. The level of overall genetic diversity was comparable between wild rice populations and rice cultivars, but a great number of wild-specific alleles was detected in the wild populations. We conclude based on the results that crop-wild introgression can considerably alter the pattern of genetic structure and relationships of CWR populations. Appropriate measures should be taken for effective in situ conservation of CWR species under the scenario of crop-wild introgression.

Utilizing inter-subspecies heterosis of indica-japonica rice hybrids is a potential solution to break the yield ceiling for hybrid rice breeding. However, the reduced panicle fertility (PF) of the inter-subspecies hybrids caused by reproductive isolation due to genetic divergence between parental varieties has hampered the effective utilization of the inter-subspecies heterosis. This is because significantly reduced fertility always leads to low yield of the F1 hybrids. To study the association between genetic divergence of indica-japonica parental varieties and panicle fertility of their inter-subspecies hybrids, we developed a method to determine the genetic divergence index (GDI) of the two parents, assisted by the insertion/deletion (InDel) molecular genotyping. Based on parents’ GDI, we produced 103 combinations of F1 hybrids whose parental varieties showed a wide range of indica-japonica genetic divergence. PF of all the F1 hybrids in different combinations was measured to analyze its association with GDI of their corresponding parents. A negative correlation between GDI of indica-japonica parental varieties and PF of their corresponding F1 hybrids was detected based on field experiments conducted in three independent locations. The results suggested that GDI of parental varieties can be used to predict PF of their indica-japonica hybrids before a hybridization experiment is conducted. The molecular-maker-based GDI provides a useful tool to assist in selecting indica and japonica parental varieties for hybrid rice breeding in a more designed manner to achieve reasonable heterosis and panicle fertilities in F1 hybrids.

DNA polymorphisms from nucleotide insertion/deletions (InDels) in genomic sequences are the basis for developing InDel molecular markers. To validate the InDel primer pairs on the basis of the comparative genomic study on DNA sequences between an Indica rice 93-11 and a Japonica rice Nipponbare for identifying Indica and Japonica rice varieties and studying wild Oryza species, we studied 49 Indica, 43 Japonica, and 24 wild rice accessions collected from ten Asian countries using 45 InDel primer pairs. Results indicated that of the 45 InDel primer pairs, 41 can accurately identify Indica and Japonica rice varieties with a reliability of over 80%. The scatter plotting data of the principal component analysis (PCA) indicated that: (i) the InDel primer pairs can easily distinguish Indica from Japonica rice varieties, in addition to revealing their genetic differentiation; (ii) the AA-genome wild rice species showed a relatively close genetic relationship with the Indica rice varieties; and (iii) the non-AA genome wild rice species did not show evident differentiation into the Indica and Japonica types. It is concluded from the study that most of the InDel primer pairs obtained from DNA sequences of 93-11 and Nipponbare can be used for identifying Indica and Japonica rice varieties, and for studying genetic relationships of wild rice species, particularly in terms of the Indica-Japonica differentiation.